$ACGL
ARCH CAPITAL GROUP LTD. Stock $acgl

$acgl Overview Financials Valuation SEC Filings Company Website

2021 Q4 Form 10-K Financial Statement

#000094748422000015 Filed on February 25, 2022

Income Statement

Concept	2021 Q4	2021	2020 Q4
Revenue	$2.246B	$9.250B	$2.297B
YoY Change	-2.24%	8.71%	33.78%
Cost Of Revenue		$4.585B
YoY Change		-2.23%
Gross Profit		$4.665B
YoY Change		22.16%
Gross Profit Margin		50.43%
Selling, General & Admin	$18.15M	$79.16M	$25.30M
YoY Change	-28.26%	-3.47%	-5.6%
% of Gross Profit		1.7%
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$33.13M	$1.303B	$19.20M
YoY Change	72.56%	29.69%	-12.33%
% of Gross Profit		27.93%
Operating Expenses	$1.666B	$7.049B	$1.642B
YoY Change	1.46%	4.88%	24.42%
Operating Profit		-$2.384B
YoY Change		-17.86%
Interest Expense	$38.05M	$139.5M	-$21.30M
YoY Change	-278.62%	-2.78%	-62.23%
% of Operating Profit
Other Income/Expense, Net		$998.6M
YoY Change		14.1%
Pretax Income	$617.4M	$2.368B	$633.4M
YoY Change	-2.52%	50.11%	86.24%
Income Tax	$34.41M	$128.6M	$34.10M
% Of Pretax Income	5.57%	5.43%	5.38%
Net Earnings	$623.3M	$2.157B	$543.5M
YoY Change	14.67%	53.46%	66.54%
Net Earnings / Revenue	27.75%	23.32%	23.66%
Basic Earnings Per Share		$5.34	$1.32
Diluted Earnings Per Share	$1.604M	$5.23	$1.30
COMMON SHARES
Basic Shares Outstanding	386.1M shares	391.7M shares	406.0M shares
Diluted Shares Outstanding		400.3M shares

Balance Sheet

Concept	2021 Q4	2021	2020 Q4
SHORT-TERM ASSETS
Cash & Short-Term Investments
YoY Change
Cash & Equivalents	$858.7M		$906.4M
Short-Term Investments
Other Short-Term Assets
YoY Change
Inventory
Prepaid Expenses
Receivables
Other Receivables
Total Short-Term Assets
YoY Change
LONG-TERM ASSETS
Property, Plant & Equipment	$106.8M	$106.8M	$116.0M
YoY Change	-7.9%	-7.9%	-12.12%
Goodwill	$344.9M		$314.6M
YoY Change	9.61%		-3.65%
Intangibles
YoY Change
Long-Term Investments	$3.078B	$27.72B	$2.048B
YoY Change	50.28%	-2.59%	23.34%
Other Assets	$456.1M	$456.1M	$384.0M
YoY Change	18.78%	18.78%
Total Long-Term Assets
YoY Change
TOTAL ASSETS
Total Short-Term Assets
Total Long-Term Assets
Total Assets	$45.10B	$45.10B	$43.28B
YoY Change	4.2%	4.2%	14.25%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable
YoY Change
Accrued Expenses	$126.7M	$126.7M	$136.0M
YoY Change	-6.83%	-6.83%	-9.93%
Deferred Revenue
YoY Change
Short-Term Debt	$0.00	$0.00	$0.00
YoY Change
Long-Term Debt Due
YoY Change
Total Short-Term Liabilities	$191.6M	$191.6M	$355.0M
YoY Change	-46.04%	-46.04%	48.54%
LONG-TERM LIABILITIES
Long-Term Debt	$2.724B	$2.724B	$3.017B
YoY Change	-9.7%	-9.7%	28.06%
Other Long-Term Liabilities	$1.445B	$1.445B	$1.892B
YoY Change	-23.61%	-23.61%	-3.37%
Total Long-Term Liabilities	$4.170B	$4.170B	$4.909B
YoY Change	-15.06%	-15.06%	13.79%
TOTAL LIABILITIES
Total Short-Term Liabilities	$191.6M	$191.6M	$355.0M
Total Long-Term Liabilities	$4.170B	$4.170B	$4.909B
Total Liabilities	$31.55B	$31.56B	$29.29B
YoY Change	7.68%	4.57%	14.57%
SHAREHOLDERS EQUITY
Retained Earnings	$14.46B		$12.36B
YoY Change	16.93%		12.17%
Common Stock	$2.086B		$1.978B
YoY Change	5.42%		4.66%
Preferred Stock
YoY Change
Treasury Stock (at cost)	$3.761B		$2.504B
YoY Change	50.21%		4.07%
Treasury Stock Shares	204.4M shares		172.3M shares
Shareholders Equity	$13.55B	$13.55B	$13.11B
YoY Change
Total Liabilities & Shareholders Equity	$45.10B	$45.10B	$43.28B
YoY Change	4.2%	4.2%	14.25%

Cashflow Statement

Concept	2021 Q4	2021	2020 Q4
OPERATING ACTIVITIES
Net Income	$623.3M	$2.157B	$543.5M
YoY Change	14.67%	53.46%	66.54%
Depreciation, Depletion And Amortization	$33.13M	$1.303B	$19.20M
YoY Change	72.56%	29.69%	-12.33%
Cash From Operating Activities	$800.0M	$3.428B	$555.0M
YoY Change	44.14%	18.74%	9.81%
INVESTING ACTIVITIES
Capital Expenditures	-$6.987M	-$41.39M	-$13.20M
YoY Change	-47.07%	3.74%	29.41%
Acquisitions
YoY Change
Other Investing Activities	-$679.5M	$523.9M	-$421.7M
YoY Change	61.12%	742.27%	-22.74%
Cash From Investing Activities	-$686.4M	-$2.140B	-$434.8M
YoY Change	57.88%	-29.69%	-21.8%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net		$1.234B
YoY Change		1378.69%
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	-347.7M	-$1.230B	-44.80M
YoY Change	676.05%	-335.87%	30.99%
NET CHANGE
Cash From Operating Activities	800.0M	$3.428B	555.0M
Cash From Investing Activities	-686.4M	-$2.140B	-434.8M
Cash From Financing Activities	-347.7M	-$1.230B	-44.80M
Net Change In Cash	-234.1M	$24.23M	75.40M
YoY Change	-410.5%	-93.74%	-188.92%
FREE CASH FLOW
Cash From Operating Activities	$800.0M	$3.428B	$555.0M
Capital Expenditures	-$6.987M	-$41.39M	-$13.20M
Free Cash Flow	$807.0M	$3.469B	$568.2M
YoY Change	42.03%	18.54%	10.2%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
CY2021	dei	Entity Central Index Key EntityCentralIndexKey	0000947484
CY2021	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2020
CY2021	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2021	dei	Amendment Flag AmendmentFlag	false
CY2020	us-gaap	Accounting Standards Update Extensible List AccountingStandardsUpdateExtensibleList	http://fasb.org/us-gaap/2021-01-31#AccountingStandardsUpdate201613Member
CY2021	acgl	Equity Method Investments Time Lag For Reporting Low Endof Range EquityMethodInvestmentsTimeLagForReportingLowEndofRange	P1M
CY2021	acgl	Equity Method Investments Time Lag For Reporting High Endof Range EquityMethodInvestmentsTimeLagForReportingHighEndofRange	P3M
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Award Vesting Period1 ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1	P3Y0M
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Award Requisite Service Period1 ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1	P3Y0M
CY2021	acgl	Equity Method Investments Time Lag For Reporting Low Endof Range EquityMethodInvestmentsTimeLagForReportingLowEndofRange	P1M
CY2021	acgl	Equity Method Investments Time Lag For Reporting High Endof Range EquityMethodInvestmentsTimeLagForReportingHighEndofRange	P3M
CY2021	acgl	Equity Method Investments Time Lag For Reporting High Endof Range EquityMethodInvestmentsTimeLagForReportingHighEndofRange	P3M
CY2021Q4	us-gaap	Operating Lease Liability Statement Of Financial Position Extensible List OperatingLeaseLiabilityStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2021-01-31#OtherLiabilities
CY2021Q4	us-gaap	Operating Lease Right Of Use Asset Statement Of Financial Position Extensible List OperatingLeaseRightOfUseAssetStatementOfFinancialPositionExtensibleList	http://fasb.org/us-gaap/2021-01-31#OtherAssets
CY2021	dei	Document Type DocumentType	10-K
CY2021	dei	Document Annual Report DocumentAnnualReport	true
CY2021	dei	Document Transition Report DocumentTransitionReport	false
CY2021	dei	Document Period End Date DocumentPeriodEndDate	2021-12-31
CY2021	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2021	dei	Entity File Number EntityFileNumber	001-16209
CY2021	dei	Entity Registrant Name EntityRegistrantName	ARCH CAPITAL GROUP LTD.
CY2021	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	D0
CY2021	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	98-0374481
CY2021	dei	Entity Address Address Line1 EntityAddressAddressLine1	Waterloo House, Ground Floor
CY2021	dei	Entity Address Address Line2 EntityAddressAddressLine2	100 Pitts Bay Road,
CY2021	dei	Entity Address City Or Town EntityAddressCityOrTown	Pembroke
CY2021	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	HM 08,
CY2021	dei	Entity Address Country EntityAddressCountry	BM
CY2021	dei	City Area Code CityAreaCode	(441)
CY2021	dei	Local Phone Number LocalPhoneNumber	278-9250
CY2021	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	Yes
CY2021	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2021	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2021	dei	Entity Interactive Data Current EntityInteractiveDataCurrent	Yes
CY2021	dei	Entity Shell Company EntityShellCompany	false
CY2021Q2	dei	Entity Public Float EntityPublicFloat	14300000000	USD
CY2022Q1	dei	Entity Common Stock Shares Outstanding EntityCommonStockSharesOutstanding	379042099	shares
CY2021	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
CY2021	dei	Entity Small Business EntitySmallBusiness	false
CY2021	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
CY2021	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
CY2021	dei	Icfr Auditor Attestation Flag IcfrAuditorAttestationFlag	true
CY2021	dei	Auditor Firm AuditorFirmId	238
CY2021	dei	Auditor Name AuditorName	PricewaterhouseCoopers LLP
CY2021	dei	Auditor Location AuditorLocation	New York, New York
CY2021Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	17973823000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	18143305000	USD
CY2021Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	17998109000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	18717825000	USD
CY2021Q4	acgl	Short Term Investments Cost Amount ShortTermInvestmentsCostAmount	1734738000	USD
CY2020Q4	acgl	Short Term Investments Cost Amount ShortTermInvestmentsCostAmount	1924292000	USD
CY2021Q4	us-gaap	Other Short Term Investments OtherShortTermInvestments	1734716000	USD
CY2020Q4	us-gaap	Other Short Term Investments OtherShortTermInvestments	1924922000	USD
CY2021Q4	acgl	Securities Received As Collateral Amortized Cost SecuritiesReceivedAsCollateralAmortizedCost	0	USD
CY2020Q4	acgl	Securities Received As Collateral Amortized Cost SecuritiesReceivedAsCollateralAmortizedCost	301089000	USD
CY2021Q4	us-gaap	Securities Received As Collateral SecuritiesReceivedAsCollateral	0	USD
CY2020Q4	us-gaap	Securities Received As Collateral SecuritiesReceivedAsCollateral	301096000	USD
CY2021Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	1804170000	USD
CY2020Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	1444830000	USD
CY2021Q4	acgl	Investments Accounted For Using Fair Value Option InvestmentsAccountedForUsingFairValueOption	1973550000	USD
CY2020Q4	acgl	Investments Accounted For Using Fair Value Option InvestmentsAccountedForUsingFairValueOption	3824796000	USD
CY2021Q4	us-gaap	Other Investments OtherInvestments	1973550000	USD
CY2020Q4	us-gaap	Other Investments OtherInvestments	4324796000	USD
CY2021Q4	us-gaap	Equity Method Investments EquityMethodInvestments	3077611000	USD
CY2020Q4	acgl	Intangible Assets Liabilitiesand Goodwill Net IntangibleAssetsLiabilitiesandGoodwillNet	692863000	USD
CY2020Q4	us-gaap	Equity Method Investments EquityMethodInvestments	2047889000	USD
CY2021Q4	us-gaap	Investments Investments	26588156000	USD
CY2020Q4	us-gaap	Investments Investments	28761358000	USD
CY2021Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	858668000	USD
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	906448000	USD
CY2021Q4	us-gaap	Accrued Investment Income Receivable AccruedInvestmentIncomeReceivable	85453000	USD
CY2020Q4	us-gaap	Accrued Investment Income Receivable AccruedInvestmentIncomeReceivable	103299000	USD
CY2021Q4	acgl	Securities Lending Investments Pledged Amortized Cost SecuritiesLendingInvestmentsPledgedAmortizedCost	0	USD
CY2020Q4	acgl	Securities Lending Investments Pledged Amortized Cost SecuritiesLendingInvestmentsPledgedAmortizedCost	294493000	USD
CY2021Q4	acgl	Fixed Maturities And Short Term Investments Pledged Under Securities Lending Fair Value FixedMaturitiesAndShortTermInvestmentsPledgedUnderSecuritiesLendingFairValue	0	USD
CY2020Q4	acgl	Fixed Maturities And Short Term Investments Pledged Under Securities Lending Fair Value FixedMaturitiesAndShortTermInvestmentsPledgedUnderSecuritiesLendingFairValue	294912000	USD
CY2021Q4	acgl	Investment In Operating Affiliate Equity Method InvestmentInOperatingAffiliateEquityMethod	1135655000	USD
CY2020Q4	acgl	Investment In Operating Affiliate Equity Method InvestmentInOperatingAffiliateEquityMethod	129291000	USD
CY2021Q4	us-gaap	Premiums Receivable Allowance For Doubtful Accounts PremiumsReceivableAllowanceForDoubtfulAccounts	39958000	USD
CY2020Q4	us-gaap	Premiums Receivable Allowance For Doubtful Accounts PremiumsReceivableAllowanceForDoubtfulAccounts	37781000	USD
CY2021Q4	us-gaap	Premiums Receivable At Carrying Value PremiumsReceivableAtCarryingValue	2633280000	USD
CY2020Q4	us-gaap	Premiums Receivable At Carrying Value PremiumsReceivableAtCarryingValue	2064586000	USD
CY2021Q4	us-gaap	Reinsurance Recoverables Allowance ReinsuranceRecoverablesAllowance	13230000	USD
CY2020Q4	us-gaap	Reinsurance Recoverables Allowance ReinsuranceRecoverablesAllowance	11636000	USD
CY2021Q4	us-gaap	Reinsurance Recoverables On Paid And Unpaid Losses ReinsuranceRecoverablesOnPaidAndUnpaidLosses	5880735000	USD
CY2020Q4	us-gaap	Reinsurance Recoverables On Paid And Unpaid Losses ReinsuranceRecoverablesOnPaidAndUnpaidLosses	4500802000	USD
CY2021Q4	us-gaap	Contract With Customer Asset Accumulated Allowance For Credit Loss ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss	3437000	USD
CY2020Q4	us-gaap	Contract With Customer Asset Accumulated Allowance For Credit Loss ContractWithCustomerAssetAccumulatedAllowanceForCreditLoss	8638000	USD
CY2021Q4	acgl	Contractholder Deductibles Receivable ContractholderDeductiblesReceivable	1828691000	USD
CY2020Q4	acgl	Contractholder Deductibles Receivable ContractholderDeductiblesReceivable	1986924000	USD
CY2021Q4	us-gaap	Prepaid Reinsurance Premiums PrepaidReinsurancePremiums	1729455000	USD
CY2020Q4	us-gaap	Prepaid Reinsurance Premiums PrepaidReinsurancePremiums	1234075000	USD
CY2021Q4	us-gaap	Deferred Policy Acquisition Costs DeferredPolicyAcquisitionCosts	901841000	USD
CY2020Q4	us-gaap	Deferred Policy Acquisition Costs DeferredPolicyAcquisitionCosts	790708000	USD
CY2021Q4	us-gaap	Receivables From Brokers Dealers And Clearing Organizations ReceivablesFromBrokersDealersAndClearingOrganizations	60179000	USD
CY2020Q4	us-gaap	Receivables From Brokers Dealers And Clearing Organizations ReceivablesFromBrokersDealersAndClearingOrganizations	92743000	USD
CY2021Q4	acgl	Intangible Assets Liabilitiesand Goodwill Net IntangibleAssetsLiabilitiesandGoodwillNet	944983000	USD
CY2020	us-gaap	Marketable Securities Gain Loss Excluding Other Than Temporary Impairments MarketableSecuritiesGainLossExcludingOtherThanTemporaryImpairments	823460000	USD
CY2021Q4	us-gaap	Other Assets OtherAssets	2453849000	USD
CY2020Q4	us-gaap	Other Assets OtherAssets	1724288000	USD
CY2021Q4	us-gaap	Assets Assets	45100945000	USD
CY2020Q4	us-gaap	Assets Assets	43282297000	USD
CY2021Q4	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	17757156000	USD
CY2020Q4	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	16513929000	USD
CY2021Q4	us-gaap	Unearned Premiums UnearnedPremiums	6011942000	USD
CY2020Q4	us-gaap	Unearned Premiums UnearnedPremiums	4838965000	USD
CY2021Q4	us-gaap	Reinsurance Payable ReinsurancePayable	1583253000	USD
CY2020Q4	us-gaap	Reinsurance Payable ReinsurancePayable	683263000	USD
CY2021Q4	acgl	Contract Holder Payables ContractHolderPayables	1832127000	USD
CY2020Q4	acgl	Contract Holder Payables ContractHolderPayables	1995562000	USD
CY2021Q4	us-gaap	Policyholder Contract Deposits PolicyholderContractDeposits	242352000	USD
CY2020Q4	us-gaap	Policyholder Contract Deposits PolicyholderContractDeposits	215581000	USD
CY2021Q4	us-gaap	Senior Long Term Notes SeniorLongTermNotes	2724394000	USD
CY2020Q4	us-gaap	Senior Long Term Notes SeniorLongTermNotes	2861113000	USD
CY2021Q4	us-gaap	Line Of Credit LineOfCredit	0	USD
CY2020Q4	us-gaap	Line Of Credit LineOfCredit	155687000	USD
CY2021Q4	us-gaap	Obligation To Return Securities Received As Collateral ObligationToReturnSecuritiesReceivedAsCollateral	0	USD
CY2020Q4	us-gaap	Obligation To Return Securities Received As Collateral ObligationToReturnSecuritiesReceivedAsCollateral	301089000	USD
CY2021Q4	srt	Payables To Broker Dealers And Clearing Organizations PayablesToBrokerDealersAndClearingOrganizations	64850000	USD
CY2020Q4	srt	Payables To Broker Dealers And Clearing Organizations PayablesToBrokerDealersAndClearingOrganizations	218779000	USD
CY2021Q4	us-gaap	Other Liabilities OtherLiabilities	1329742000	USD
CY2020Q4	us-gaap	Other Liabilities OtherLiabilities	1510888000	USD
CY2021Q4	us-gaap	Liabilities Liabilities	31545816000	USD
CY2020Q4	us-gaap	Liabilities Liabilities	29294856000	USD
CY2021Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies		USD
CY2020Q4	us-gaap	Commitments And Contingencies CommitmentsAndContingencies		USD
CY2021Q4	us-gaap	Redeemable Noncontrolling Interest Equity Fair Value RedeemableNoncontrollingInterestEquityFairValue	9233000	USD
CY2020Q4	us-gaap	Redeemable Noncontrolling Interest Equity Fair Value RedeemableNoncontrollingInterestEquityFairValue	58548000	USD
CY2021Q4	us-gaap	Preferred Stock Value PreferredStockValue	830000000	USD
CY2020Q4	us-gaap	Preferred Stock Value PreferredStockValue	780000000	USD
CY2020Q4	us-gaap	Common Stock Par Or Stated Value Per Share CommonStockParOrStatedValuePerShare	0.0011
CY2021Q4	us-gaap	Common Stock Par Or Stated Value Per Share CommonStockParOrStatedValuePerShare	0.0011
CY2021Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	583289850	shares
CY2020Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	579000841	shares
CY2021Q4	us-gaap	Common Stock Value CommonStockValue	648000	USD
CY2020Q4	us-gaap	Common Stock Value CommonStockValue	643000	USD
CY2021Q4	us-gaap	Additional Paid In Capital Common Stock AdditionalPaidInCapitalCommonStock	2085075000	USD
CY2020Q4	us-gaap	Additional Paid In Capital Common Stock AdditionalPaidInCapitalCommonStock	1977794000	USD
CY2021Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	14455868000	USD
CY2020Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	12362463000	USD
CY2021Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-64600000	USD
CY2020Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	488895000	USD
CY2021Q4	us-gaap	Treasury Stock Shares TreasuryStockShares	204365956	shares
CY2020Q4	us-gaap	Treasury Stock Shares TreasuryStockShares	172280199	shares
CY2021Q4	us-gaap	Treasury Stock Value TreasuryStockValue	3761095000	USD
CY2020Q4	us-gaap	Treasury Stock Value TreasuryStockValue	2503909000	USD
CY2021Q4	us-gaap	Stockholders Equity StockholdersEquity	13545896000	USD
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	13105886000	USD
CY2021Q4	us-gaap	Minority Interest MinorityInterest	0	USD
CY2020Q4	us-gaap	Minority Interest MinorityInterest	823007000	USD
CY2021Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	13545896000	USD
CY2020Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	13928893000	USD
CY2021Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	45100945000	USD
CY2020Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	43282297000	USD
CY2021	us-gaap	Premiums Earned Net PremiumsEarnedNet	8082298000	USD
CY2020	us-gaap	Premiums Earned Net PremiumsEarnedNet	6991935000	USD
CY2019	us-gaap	Premiums Earned Net PremiumsEarnedNet	5786498000	USD
CY2021	us-gaap	Investment Income Net InvestmentIncomeNet	389118000	USD
CY2020	us-gaap	Investment Income Net InvestmentIncomeNet	519608000	USD
CY2019	us-gaap	Investment Income Net InvestmentIncomeNet	627738000	USD
CY2021	us-gaap	Marketable Securities Gain Loss Excluding Other Than Temporary Impairments MarketableSecuritiesGainLossExcludingOtherThanTemporaryImpairments	379845000	USD
CY2019	us-gaap	Marketable Securities Gain Loss Excluding Other Than Temporary Impairments MarketableSecuritiesGainLossExcludingOtherThanTemporaryImpairments	363198000	USD
CY2021	us-gaap	Insurance Commissions And Fees InsuranceCommissionsAndFees	22073000	USD
CY2020	us-gaap	Insurance Commissions And Fees InsuranceCommissionsAndFees	26784000	USD
CY2019	us-gaap	Insurance Commissions And Fees InsuranceCommissionsAndFees	24861000	USD
CY2021	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	366402000	USD
CY2020	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	146693000	USD
CY2019	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	123672000	USD
CY2021	us-gaap	Other Operating Income Expense Net OtherOperatingIncomeExpenseNet	10244000	USD
CY2020	us-gaap	Other Operating Income Expense Net OtherOperatingIncomeExpenseNet	29000	USD
CY2019	us-gaap	Other Operating Income Expense Net OtherOperatingIncomeExpenseNet	0	USD
CY2021	us-gaap	Revenues Revenues	9249980000	USD
CY2020	us-gaap	Revenues Revenues	8508509000	USD
CY2019	us-gaap	Revenues Revenues	6925967000	USD
CY2021	us-gaap	Policyholder Benefits And Claims Incurred Net PolicyholderBenefitsAndClaimsIncurredNet	4584803000	USD
CY2020	us-gaap	Policyholder Benefits And Claims Incurred Net PolicyholderBenefitsAndClaimsIncurredNet	4689599000	USD
CY2019	us-gaap	Policyholder Benefits And Claims Incurred Net PolicyholderBenefitsAndClaimsIncurredNet	3133452000	USD
CY2021	us-gaap	Deferred Policy Acquisition Cost Amortization Expense DeferredPolicyAcquisitionCostAmortizationExpense	1303178000	USD
CY2020	us-gaap	Deferred Policy Acquisition Cost Amortization Expense DeferredPolicyAcquisitionCostAmortizationExpense	1004842000	USD
CY2019	us-gaap	Deferred Policy Acquisition Cost Amortization Expense DeferredPolicyAcquisitionCostAmortizationExpense	840945000	USD
CY2021	us-gaap	Other Cost And Expense Operating OtherCostAndExpenseOperating	998595000	USD
CY2020	us-gaap	Other Cost And Expense Operating OtherCostAndExpenseOperating	875176000	USD
CY2019	us-gaap	Other Cost And Expense Operating OtherCostAndExpenseOperating	800997000	USD
CY2021	us-gaap	General And Administrative Expense GeneralAndAdministrativeExpense	79157000	USD
CY2020	us-gaap	General And Administrative Expense GeneralAndAdministrativeExpense	81988000	USD
CY2019	us-gaap	General And Administrative Expense GeneralAndAdministrativeExpense	80111000	USD
CY2021	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	82955000	USD
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	69031000	USD
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	82104000	USD
CY2021	us-gaap	Interest Expense InterestExpense	139470000	USD
CY2020	us-gaap	Interest Expense InterestExpense	143456000	USD
CY2019	us-gaap	Interest Expense InterestExpense	120872000	USD
CY2021	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	41529000	USD
CY2020	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	-83634000	USD
CY2019	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	-20609000	USD
CY2019	acgl	Income Loss From Continuing Operations Before Earnings From Affiliates Income Taxes Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeEarningsFromAffiliatesIncomeTaxesNoncontrollingInterest	1846877000	USD
CY2021	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	7146629000	USD
CY2020	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	6947726000	USD
CY2019	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	5079090000	USD
CY2021	acgl	Income Loss From Continuing Operations Before Earnings From Affiliates Income Taxes Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeEarningsFromAffiliatesIncomeTaxesNoncontrollingInterest	2103351000	USD
CY2020	acgl	Income Loss From Continuing Operations Before Earnings From Affiliates Income Taxes Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeEarningsFromAffiliatesIncomeTaxesNoncontrollingInterest	1560783000	USD
CY2021	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	295533000	USD
CY2020	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	197662000	USD
CY2019	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	144361000	USD
CY2021	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-166951000	USD
CY2020	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-85824000	USD
CY2019	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	11449000	USD
CY2021	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	128582000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	111838000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	155810000	USD
CY2021	acgl	Income Loss From Operating Affiliates Equity Method IncomeLossFromOperatingAffiliatesEquityMethod	264693000	USD
CY2020	acgl	Income Loss From Operating Affiliates Equity Method IncomeLossFromOperatingAffiliatesEquityMethod	16766000	USD
CY2019	acgl	Income Loss From Operating Affiliates Equity Method IncomeLossFromOperatingAffiliatesEquityMethod	2233000	USD
CY2021	us-gaap	Profit Loss ProfitLoss	2239462000	USD
CY2020	us-gaap	Profit Loss ProfitLoss	1465711000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	1693300000	USD
CY2021	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	82613000	USD
CY2020	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	60190000	USD
CY2019	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	56981000	USD
CY2021	us-gaap	Net Income Loss NetIncomeLoss	2156849000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	1405521000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	1636319000	USD
CY2021	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	48343000	USD
CY2020	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	41612000	USD
CY2019	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	41612000	USD
CY2021	us-gaap	Preferred Stock Redemption Premium PreferredStockRedemptionPremium	15101000	USD
CY2020	us-gaap	Preferred Stock Redemption Premium PreferredStockRedemptionPremium	0	USD
CY2019	us-gaap	Preferred Stock Redemption Premium PreferredStockRedemptionPremium	0	USD
CY2021	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	2093405000	USD
CY2020	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	1363909000	USD
CY2019	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	1594707000	USD
CY2021	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	5.34
CY2020	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.38
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.97
CY2021	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	5.23
CY2020	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.32
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.87
CY2021	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	391748715	shares
CY2020	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	403062179	shares
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	401802815	shares
CY2021	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	400345936	shares
CY2020	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	410259455	shares
CY2019	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	411609478	shares
CY2021	us-gaap	Profit Loss ProfitLoss	2239462000	USD
CY2020	us-gaap	Profit Loss ProfitLoss	1465711000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	1693300000	USD
CY2021	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	-386929000	USD
CY2020	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	678717000	USD
CY2019	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	500771000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax	116068000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax	426187000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesNetOfTax	118941000	USD
CY2021	us-gaap	Other Comprehensive Income Foreign Currency Transaction And Translation Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax	-64482000	USD
CY2020	us-gaap	Other Comprehensive Income Foreign Currency Transaction And Translation Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax	33336000	USD
CY2019	us-gaap	Other Comprehensive Income Foreign Currency Transaction And Translation Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax	18110000	USD
CY2021	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	1671983000	USD
CY2020	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	1751577000	USD
CY2019	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	2093240000	USD
CY2021	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	82613000	USD
CY2020	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	60190000	USD
CY2019	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	56981000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Noncontrolling Interest OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest	-13984000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Noncontrolling Interest OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest	9062000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Noncontrolling Interest OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToNoncontrollingInterest	9130000	USD
CY2021	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	1603354000	USD
CY2020	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	1682325000	USD
CY2019	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	2027129000	USD
CY2021Q4	us-gaap	Stockholders Equity StockholdersEquity	13545896000	USD
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	13105886000	USD
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	11497371000	USD
CY2021Q4	us-gaap	Minority Interest MinorityInterest	0	USD
CY2020Q4	us-gaap	Minority Interest MinorityInterest	823007000	USD
CY2019Q4	us-gaap	Minority Interest MinorityInterest	762777000	USD
CY2021Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	13545896000	USD
CY2020Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	13928893000	USD
CY2019Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	12260148000	USD
CY2021	us-gaap	Profit Loss ProfitLoss	2239462000	USD
CY2020	us-gaap	Profit Loss ProfitLoss	1465711000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	1693300000	USD
CY2021	acgl	Net Realized Gains Losses NetRealizedGainsLosses	427367000	USD
CY2020	acgl	Net Realized Gains Losses NetRealizedGainsLosses	844625000	USD
CY2019	acgl	Net Realized Gains Losses NetRealizedGainsLosses	377967000	USD
CY2021	acgl	Equity In Net Income Loss Of Investment Funds Accounted For Using Equity Method And Other Income Loss EquityInNetIncomeLossOfInvestmentFundsAccountedForUsingEquityMethodAndOtherIncomeLoss	464050000	USD
CY2020	acgl	Equity In Net Income Loss Of Investment Funds Accounted For Using Equity Method And Other Income Loss EquityInNetIncomeLossOfInvestmentFundsAccountedForUsingEquityMethodAndOtherIncomeLoss	47951000	USD
CY2019	acgl	Equity In Net Income Loss Of Investment Funds Accounted For Using Equity Method And Other Income Loss EquityInNetIncomeLossOfInvestmentFundsAccountedForUsingEquityMethodAndOtherIncomeLoss	14013000	USD
CY2021	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	82955000	USD
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	69031000	USD
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	82104000	USD
CY2021	us-gaap	Share Based Compensation ShareBasedCompensation	87094000	USD
CY2019	us-gaap	Increase Decrease In Reinsurance Payables IncreaseDecreaseInReinsurancePayables	182132000	USD
CY2021	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	340376000	USD
CY2020	us-gaap	Share Based Compensation ShareBasedCompensation	71262000	USD
CY2019	us-gaap	Share Based Compensation ShareBasedCompensation	66417000	USD
CY2021	acgl	Increase Decrease In Loss And Loss Adjustment Expenses Net Of Recoverables IncreaseDecreaseInLossAndLossAdjustmentExpensesNetOfRecoverables	1762190000	USD
CY2020	acgl	Increase Decrease In Loss And Loss Adjustment Expenses Net Of Recoverables IncreaseDecreaseInLossAndLossAdjustmentExpensesNetOfRecoverables	2113827000	USD
CY2019	acgl	Increase Decrease In Loss And Loss Adjustment Expenses Net Of Recoverables IncreaseDecreaseInLossAndLossAdjustmentExpensesNetOfRecoverables	489981000	USD
CY2021	acgl	Increase Decrease In Unearned Premiums Net Of Prepaid Reinsurance Premiums IncreaseDecreaseInUnearnedPremiumsNetOfPrepaidReinsurancePremiums	936039000	USD
CY2020	acgl	Increase Decrease In Unearned Premiums Net Of Prepaid Reinsurance Premiums IncreaseDecreaseInUnearnedPremiumsNetOfPrepaidReinsurancePremiums	445781000	USD
CY2019	acgl	Increase Decrease In Unearned Premiums Net Of Prepaid Reinsurance Premiums IncreaseDecreaseInUnearnedPremiumsNetOfPrepaidReinsurancePremiums	252569000	USD
CY2021	us-gaap	Increase Decrease In Premiums Receivable IncreaseDecreaseInPremiumsReceivable	685214000	USD
CY2020	us-gaap	Increase Decrease In Premiums Receivable IncreaseDecreaseInPremiumsReceivable	318643000	USD
CY2019	us-gaap	Increase Decrease In Premiums Receivable IncreaseDecreaseInPremiumsReceivable	237752000	USD
CY2021	us-gaap	Increase Decrease In Deferred Policy Acquisition Costs IncreaseDecreaseInDeferredPolicyAcquisitionCosts	263243000	USD
CY2020	us-gaap	Increase Decrease In Deferred Policy Acquisition Costs IncreaseDecreaseInDeferredPolicyAcquisitionCosts	143948000	USD
CY2019	us-gaap	Increase Decrease In Deferred Policy Acquisition Costs IncreaseDecreaseInDeferredPolicyAcquisitionCosts	47260000	USD
CY2021	us-gaap	Increase Decrease In Reinsurance Payables IncreaseDecreaseInReinsurancePayables	500065000	USD
CY2020	us-gaap	Increase Decrease In Reinsurance Payables IncreaseDecreaseInReinsurancePayables	65950000	USD
CY2020	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	-10110000	USD
CY2019	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	41052000	USD
CY2021	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	3427555000	USD
CY2020	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	2886505000	USD
CY2019	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	2048459000	USD
CY2021	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	35451858000	USD
CY2020	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	39765277000	USD
CY2019	us-gaap	Payments To Acquire Available For Sale Securities Debt PaymentsToAcquireAvailableForSaleSecuritiesDebt	30053777000	USD
CY2021	us-gaap	Payments To Acquire Trading Securities Heldforinvestment PaymentsToAcquireTradingSecuritiesHeldforinvestment	1175480000	USD
CY2020	us-gaap	Payments To Acquire Trading Securities Heldforinvestment PaymentsToAcquireTradingSecuritiesHeldforinvestment	1595010000	USD
CY2019	us-gaap	Payments To Acquire Trading Securities Heldforinvestment PaymentsToAcquireTradingSecuritiesHeldforinvestment	811967000	USD
CY2021	us-gaap	Payments To Acquire Other Investments PaymentsToAcquireOtherInvestments	1859096000	USD
CY2020	us-gaap	Payments To Acquire Other Investments PaymentsToAcquireOtherInvestments	1808727000	USD
CY2019	us-gaap	Payments To Acquire Other Investments PaymentsToAcquireOtherInvestments	1470545000	USD
CY2021	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	33577445000	USD
CY2020	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	37949346000	USD
CY2019	us-gaap	Proceeds From Sale Of Available For Sale Securities Debt ProceedsFromSaleOfAvailableForSaleSecuritiesDebt	28595865000	USD
CY2021	us-gaap	Proceeds From Sale Of Trading Securities Heldforinvestment ProceedsFromSaleOfTradingSecuritiesHeldforinvestment	918145000	USD
CY2020	us-gaap	Proceeds From Sale Of Trading Securities Heldforinvestment ProceedsFromSaleOfTradingSecuritiesHeldforinvestment	1147264000	USD
CY2019	us-gaap	Proceeds From Sale Of Trading Securities Heldforinvestment ProceedsFromSaleOfTradingSecuritiesHeldforinvestment	429818000	USD
CY2021	us-gaap	Proceeds From Sale Of Other Investments ProceedsFromSaleOfOtherInvestments	1765533000	USD
CY2020	us-gaap	Proceeds From Sale Of Other Investments ProceedsFromSaleOfOtherInvestments	1029578000	USD
CY2019	us-gaap	Proceeds From Sale Of Other Investments ProceedsFromSaleOfOtherInvestments	1209559000	USD
CY2021	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	1628755000	USD
CY2020	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	871134000	USD
CY2019	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	643265000	USD
CY2021	us-gaap	Payments For Proceeds From Derivative Instrument Investing Activities PaymentsForProceedsFromDerivativeInstrumentInvestingActivities	40072000	USD
CY2020	us-gaap	Payments For Proceeds From Derivative Instrument Investing Activities PaymentsForProceedsFromDerivativeInstrumentInvestingActivities	-179006000	USD
CY2019	us-gaap	Payments For Proceeds From Derivative Instrument Investing Activities PaymentsForProceedsFromDerivativeInstrumentInvestingActivities	-59982000	USD
CY2021	us-gaap	Payments For Proceeds From Short Term Investments PaymentsForProceedsFromShortTermInvestments	-165272000	USD
CY2020	us-gaap	Payments For Proceeds From Short Term Investments PaymentsForProceedsFromShortTermInvestments	1029681000	USD
CY2019	us-gaap	Payments For Proceeds From Short Term Investments PaymentsForProceedsFromShortTermInvestments	-39833000	USD
CY2021	us-gaap	Increase Decrease In Cash Collateral For Borrowed Securities IncreaseDecreaseInCashCollateralForBorrowedSecurities	0	USD
CY2020	us-gaap	Increase Decrease In Cash Collateral For Borrowed Securities IncreaseDecreaseInCashCollateralForBorrowedSecurities	-81210000	USD
CY2019	us-gaap	Increase Decrease In Cash Collateral For Borrowed Securities IncreaseDecreaseInCashCollateralForBorrowedSecurities	62193000	USD
CY2021	us-gaap	Payments To Acquire Interest In Subsidiaries And Affiliates PaymentsToAcquireInterestInSubsidiariesAndAffiliates	753916000	USD
CY2020	us-gaap	Payments To Acquire Interest In Subsidiaries And Affiliates PaymentsToAcquireInterestInSubsidiariesAndAffiliates	0	USD
CY2019	us-gaap	Payments To Acquire Interest In Subsidiaries And Affiliates PaymentsToAcquireInterestInSubsidiariesAndAffiliates	0	USD
CY2021	us-gaap	Cash Divested From Deconsolidation CashDivestedFromDeconsolidation	349202000	USD
CY2020	us-gaap	Cash Divested From Deconsolidation CashDivestedFromDeconsolidation	0	USD
CY2019	us-gaap	Cash Divested From Deconsolidation CashDivestedFromDeconsolidation	0	USD
CY2021	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	41394000	USD
CY2020	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	39872000	USD
CY2019	us-gaap	Payments To Acquire Productive Assets PaymentsToAcquireProductiveAssets	37837000	USD
CY2021	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	523864000	USD
CY2020	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	62197000	USD
CY2019	us-gaap	Payments For Proceeds From Other Investing Activities PaymentsForProceedsFromOtherInvestingActivities	348486000	USD
CY2021	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-2139732000	USD
CY2020	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-3043226000	USD
CY2019	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-1806483000	USD
CY2021	us-gaap	Proceeds From Issuance Of Preferred Stock And Preference Stock ProceedsFromIssuanceOfPreferredStockAndPreferenceStock	485821000	USD
CY2020	us-gaap	Proceeds From Issuance Of Preferred Stock And Preference Stock ProceedsFromIssuanceOfPreferredStockAndPreferenceStock	0	USD
CY2019	us-gaap	Proceeds From Issuance Of Preferred Stock And Preference Stock ProceedsFromIssuanceOfPreferredStockAndPreferenceStock	0	USD
CY2021	us-gaap	Payments For Repurchase Of Preferred Stock And Preference Stock PaymentsForRepurchaseOfPreferredStockAndPreferenceStock	450000000	USD
CY2020	us-gaap	Payments For Repurchase Of Preferred Stock And Preference Stock PaymentsForRepurchaseOfPreferredStockAndPreferenceStock	0	USD
CY2019	us-gaap	Payments For Repurchase Of Preferred Stock And Preference Stock PaymentsForRepurchaseOfPreferredStockAndPreferenceStock	0	USD
CY2021	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	1234294000	USD
CY2020	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	83472000	USD
CY2019	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	2871000	USD
CY2021	us-gaap	Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans Including Stock Options ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions	6418000	USD
CY2020	us-gaap	Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans Including Stock Options ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions	1876000	USD
CY2019	us-gaap	Proceeds From Issuance Of Shares Under Incentive And Share Based Compensation Plans Including Stock Options ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions	6203000	USD
CY2021	us-gaap	Proceeds From Other Debt ProceedsFromOtherDebt	0	USD
CY2020	us-gaap	Proceeds From Other Debt ProceedsFromOtherDebt	1018793000	USD
CY2021	us-gaap	Proceeds From Payments For Other Financing Activities ProceedsFromPaymentsForOtherFinancingActivities	-3278000	USD
CY2019	us-gaap	Proceeds From Other Debt ProceedsFromOtherDebt	200083000	USD
CY2021	us-gaap	Repayments Of Other Debt RepaymentsOfOtherDebt	0	USD
CY2020	us-gaap	Repayments Of Other Debt RepaymentsOfOtherDebt	359000000	USD
CY2019	us-gaap	Repayments Of Other Debt RepaymentsOfOtherDebt	49182000	USD
CY2021	us-gaap	Increase Decrease In Cash Collateral For Loaned Securities IncreaseDecreaseInCashCollateralForLoanedSecurities	0	USD
CY2020	us-gaap	Increase Decrease In Cash Collateral For Loaned Securities IncreaseDecreaseInCashCollateralForLoanedSecurities	-81210000	USD
CY2019	us-gaap	Increase Decrease In Cash Collateral For Loaned Securities IncreaseDecreaseInCashCollateralForLoanedSecurities	62193000	USD
CY2021	us-gaap	Proceeds From Payments To Minority Shareholders ProceedsFromPaymentsToMinorityShareholders	15971000	USD
CY2020	us-gaap	Proceeds From Payments To Minority Shareholders ProceedsFromPaymentsToMinorityShareholders	-2867000	USD
CY2019	us-gaap	Proceeds From Payments To Minority Shareholders ProceedsFromPaymentsToMinorityShareholders	-75056000	USD
CY2021	us-gaap	Proceeds From Repurchase Of Redeemable Preferred Stock ProceedsFromRepurchaseOfRedeemablePreferredStock	0	USD
CY2020	us-gaap	Proceeds From Repurchase Of Redeemable Preferred Stock ProceedsFromRepurchaseOfRedeemablePreferredStock	0	USD
CY2019	us-gaap	Proceeds From Repurchase Of Redeemable Preferred Stock ProceedsFromRepurchaseOfRedeemablePreferredStock	-161882000	USD
CY2021	us-gaap	Payments Of Dividends Minority Interest PaymentsOfDividendsMinorityInterest	1907000	USD
CY2020	us-gaap	Payments Of Dividends Minority Interest PaymentsOfDividendsMinorityInterest	4945000	USD
CY2019	us-gaap	Payments Of Dividends Minority Interest PaymentsOfDividendsMinorityInterest	12515000	USD
CY2020	us-gaap	Proceeds From Payments For Other Financing Activities ProceedsFromPaymentsForOtherFinancingActivities	73715000	USD
CY2019	us-gaap	Proceeds From Payments For Other Financing Activities ProceedsFromPaymentsForOtherFinancingActivities	-6023000	USD
CY2021	us-gaap	Payments Of Dividends Preferred Stock And Preference Stock PaymentsOfDividendsPreferredStockAndPreferenceStock	48280000	USD
CY2020	us-gaap	Payments Of Dividends Preferred Stock And Preference Stock PaymentsOfDividendsPreferredStockAndPreferenceStock	41612000	USD
CY2019	us-gaap	Payments Of Dividends Preferred Stock And Preference Stock PaymentsOfDividendsPreferredStockAndPreferenceStock	41612000	USD
CY2021	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-1229549000	USD
CY2020	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	521278000	USD
CY2019	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-80662000	USD
CY2021	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	-34047000	USD
CY2020	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	22289000	USD
CY2019	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	17741000	USD
CY2021	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	24227000	USD
CY2020	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	386846000	USD
CY2019	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	179055000	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	1290544000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	903698000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	724643000	USD
CY2021Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	1314771000	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	1290544000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	903698000	USD
CY2021	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	286810000	USD
CY2020	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	202940000	USD
CY2019	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	109463000	USD
CY2021	us-gaap	Interest Paid Net InterestPaidNet	139301000	USD
CY2020	us-gaap	Interest Paid Net InterestPaidNet	133491000	USD
CY2019	us-gaap	Interest Paid Net InterestPaidNet	126945000	USD
CY2021	us-gaap	Use Of Estimates UseOfEstimates	<div style="margin-bottom:10pt;text-align:justify"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ materially from those estimates and assumptions. The Company’s principal estimates include:</span></div><div style="margin-bottom:3pt;padding-left:18pt;text-align:justify;text-indent:-18pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">The reserve for losses and loss adjustment expenses;</span></div><div style="margin-bottom:3pt;padding-left:18pt;text-align:justify;text-indent:-18pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">Reinsurance recoverable on unpaid and paid losses and loss adjustment expenses, including the provision for uncollectible amounts;</span></div><div style="margin-bottom:3pt;padding-left:18pt;text-align:justify;text-indent:-18pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">Estimates of written and earned premiums;</span></div><div style="margin-bottom:3pt;padding-left:18pt;text-align:justify;text-indent:-18pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">The valuation of the investment portfolio and assessment of allowance for credit losses;</span></div><div style="margin-bottom:3pt;padding-left:18pt;text-align:justify;text-indent:-18pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">The valuation of purchased intangible assets;</span></div><div style="margin-bottom:3pt;padding-left:18pt;text-align:justify;text-indent:-18pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">The assessment of goodwill and intangible assets for impairment; and</span></div><div style="margin-bottom:10pt;padding-left:18pt;text-align:justify;text-indent:-18pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">•</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%;padding-left:14.5pt">The valuation of deferred tax assets.</span></div>
CY2021	acgl	Premium Revenue Recognition Period PremiumRevenueRecognitionPeriod	P12M
CY2021	acgl	Securities Lending Rate Of Collateral Required SecuritiesLendingRateOfCollateralRequired	1.02
CY2021	us-gaap	Derivatives Methods Of Accounting Nonhedging Derivatives DerivativesMethodsOfAccountingNonhedgingDerivatives	<span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">The Company recognizes all derivative instruments, including embedded derivative instruments, at fair value in its consolidated balance sheets. The Company employs the use of derivative instruments within its operations to mitigate risks arising from assets and liabilities held in foreign currencies as well as part of its overall investment strategy. For such instruments, changes in assets and liabilities measured at fair value are recorded as “Net realized gains” in the consolidated statements of income. In addition, the Company’s derivative instruments include amounts related to underwriting activities where an insurance or reinsurance contract meets the accounting definition of a derivative instrument. For such contracts, changes in fair value are reflected in “Other underwriting income” in the consolidated statements of income as the underlying contract originates from the Company’s underwriting operations. For the periods ended 2021, 2020, and 2019, the Company did not designate any derivative instruments as hedges under the relevant accounting guidance. See </span><span style="color:#0000ff;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%;text-decoration:underline"><a href="#i9aa6868b2b724c09bc653e55fc47166e_175" style="color:#0000ff;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%;text-decoration:underline">note 11, “Derivative Instruments”</a></span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%"> for additional information.</span>
CY2021	us-gaap	Premiums Written Gross PremiumsWrittenGross	12752487000	USD
CY2021	us-gaap	Ceded Premiums Written CededPremiumsWritten	3734150000	USD
CY2021	us-gaap	Premiums Written Net PremiumsWrittenNet	9018337000	USD
CY2021	us-gaap	Increase Decrease In Unearned Premiums Net IncreaseDecreaseInUnearnedPremiumsNet	-936039000	USD
CY2021	us-gaap	Premiums Earned Net PremiumsEarnedNet	8082298000	USD
CY2021	us-gaap	Insurance Commissions And Fees InsuranceCommissionsAndFees	22073000	USD
CY2021	us-gaap	Policyholder Benefits And Claims Incurred Net PolicyholderBenefitsAndClaimsIncurredNet	4584803000	USD
CY2021	us-gaap	Deferred Policy Acquisition Cost Amortization Expense DeferredPolicyAcquisitionCostAmortizationExpense	1303178000	USD
CY2021	us-gaap	Other Expenses OtherExpenses	998595000	USD
CY2021	acgl	Underwriting Income Loss Segment UnderwritingIncomeLossSegment	1217795000	USD
CY2021	us-gaap	Investment Income Net InvestmentIncomeNet	389118000	USD
CY2021	us-gaap	Marketable Securities Gain Loss Excluding Other Than Temporary Impairments MarketableSecuritiesGainLossExcludingOtherThanTemporaryImpairments	379845000	USD
CY2021	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	366402000	USD
CY2021	us-gaap	Other Operating Income Expense Net OtherOperatingIncomeExpenseNet	10244000	USD
CY2021	acgl	Segment Other Cost And Expense Operating SegmentOtherCostAndExpenseOperating	77119000	USD
CY2021	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	2038000	USD
CY2021	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	82955000	USD
CY2021	us-gaap	Interest Expense InterestExpense	139470000	USD
CY2021	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	41529000	USD
CY2021	acgl	Income Loss From Continuing Operations Before Earnings From Affiliates Income Taxes Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeEarningsFromAffiliatesIncomeTaxesNoncontrollingInterest	2103351000	USD
CY2021	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	128582000	USD
CY2021	acgl	Income Loss From Operating Affiliates Equity Method IncomeLossFromOperatingAffiliatesEquityMethod	264693000	USD
CY2021	us-gaap	Profit Loss ProfitLoss	2239462000	USD
CY2021	us-gaap	Net Income Loss Attributable To Redeemable Noncontrolling Interest NetIncomeLossAttributableToRedeemableNoncontrollingInterest	4299000	USD
CY2021	us-gaap	Net Income Loss Attributable To Nonredeemable Noncontrolling Interest NetIncomeLossAttributableToNonredeemableNoncontrollingInterest	78314000	USD
CY2021	us-gaap	Net Income Loss NetIncomeLoss	2156849000	USD
CY2021	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	48343000	USD
CY2021	us-gaap	Preferred Stock Redemption Premium PreferredStockRedemptionPremium	15101000	USD
CY2021	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	2093405000	USD
CY2021	us-gaap	Loss Ratio LossRatio	0.567
CY2021	acgl	Acquisition Expense Ratio Percentage AcquisitionExpenseRatioPercentage	0.161
CY2021	acgl	Other Operating Expense Ratio Percentage OtherOperatingExpenseRatioPercentage	0.124
CY2021	acgl	Combined Ratio Percentage CombinedRatioPercentage	0.852
CY2021Q4	us-gaap	Intangible Assets Net Including Goodwill IntangibleAssetsNetIncludingGoodwill	944983000	USD
CY2021Q4	acgl	Investable Assets InvestableAssets	27442153000	USD
CY2021Q4	us-gaap	Assets Assets	45100945000	USD
CY2021Q4	us-gaap	Liabilities Liabilities	31545816000	USD
CY2020	us-gaap	Premiums Written Gross PremiumsWrittenGross	10088068000	USD
CY2020	us-gaap	Ceded Premiums Written CededPremiumsWritten	2650352000	USD
CY2020	us-gaap	Premiums Written Net PremiumsWrittenNet	7437716000	USD
CY2020	us-gaap	Increase Decrease In Unearned Premiums Net IncreaseDecreaseInUnearnedPremiumsNet	-445781000	USD
CY2020	us-gaap	Premiums Earned Net PremiumsEarnedNet	6991935000	USD
CY2020	us-gaap	Insurance Commissions And Fees InsuranceCommissionsAndFees	26784000	USD
CY2020	us-gaap	Policyholder Benefits And Claims Incurred Net PolicyholderBenefitsAndClaimsIncurredNet	4689599000	USD
CY2020	us-gaap	Deferred Policy Acquisition Cost Amortization Expense DeferredPolicyAcquisitionCostAmortizationExpense	1004842000	USD
CY2020	us-gaap	Other Expenses OtherExpenses	875176000	USD
CY2020	acgl	Underwriting Income Loss Segment UnderwritingIncomeLossSegment	449102000	USD
CY2020	us-gaap	Investment Income Net InvestmentIncomeNet	519608000	USD
CY2020	us-gaap	Marketable Securities Gain Loss Excluding Other Than Temporary Impairments MarketableSecuritiesGainLossExcludingOtherThanTemporaryImpairments	823460000	USD
CY2020	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	146693000	USD
CY2020	us-gaap	Other Operating Income Expense Net OtherOperatingIncomeExpenseNet	29000	USD
CY2020	acgl	Segment Other Cost And Expense Operating SegmentOtherCostAndExpenseOperating	68492000	USD
CY2020	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	13496000	USD
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	69031000	USD
CY2020	us-gaap	Interest Expense InterestExpense	143456000	USD
CY2020	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	-83634000	USD
CY2020	acgl	Income Loss From Continuing Operations Before Earnings From Affiliates Income Taxes Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeEarningsFromAffiliatesIncomeTaxesNoncontrollingInterest	1560783000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	111838000	USD
CY2020	acgl	Income Loss From Operating Affiliates Equity Method IncomeLossFromOperatingAffiliatesEquityMethod	16766000	USD
CY2020	us-gaap	Profit Loss ProfitLoss	1465711000	USD
CY2020	us-gaap	Net Income Loss Attributable To Redeemable Noncontrolling Interest NetIncomeLossAttributableToRedeemableNoncontrollingInterest	7114000	USD
CY2020	us-gaap	Net Income Loss Attributable To Nonredeemable Noncontrolling Interest NetIncomeLossAttributableToNonredeemableNoncontrollingInterest	53076000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	1405521000	USD
CY2020	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	41612000	USD
CY2020	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	1363909000	USD
CY2020	us-gaap	Loss Ratio LossRatio	0.671
CY2020	acgl	Acquisition Expense Ratio Percentage AcquisitionExpenseRatioPercentage	0.144
CY2020	acgl	Other Operating Expense Ratio Percentage OtherOperatingExpenseRatioPercentage	0.125
CY2020	acgl	Combined Ratio Percentage CombinedRatioPercentage	0.940
CY2020Q4	us-gaap	Intangible Assets Net Including Goodwill IntangibleAssetsNetIncludingGoodwill	692863000	USD
CY2020Q4	acgl	Investable Assets InvestableAssets	29513907000	USD
CY2020Q4	us-gaap	Assets Assets	43282297000	USD
CY2020Q4	us-gaap	Liabilities Liabilities	29294856000	USD
CY2019	us-gaap	Premiums Written Gross PremiumsWrittenGross	8138960000	USD
CY2019	us-gaap	Ceded Premiums Written CededPremiumsWritten	2099893000	USD
CY2019	us-gaap	Premiums Written Net PremiumsWrittenNet	6039067000	USD
CY2019	us-gaap	Increase Decrease In Unearned Premiums Net IncreaseDecreaseInUnearnedPremiumsNet	-252569000	USD
CY2019	us-gaap	Premiums Earned Net PremiumsEarnedNet	5786498000	USD
CY2019	us-gaap	Insurance Commissions And Fees InsuranceCommissionsAndFees	24861000	USD
CY2019	us-gaap	Policyholder Benefits And Claims Incurred Net PolicyholderBenefitsAndClaimsIncurredNet	3133452000	USD
CY2019	us-gaap	Deferred Policy Acquisition Cost Amortization Expense DeferredPolicyAcquisitionCostAmortizationExpense	840945000	USD
CY2019	us-gaap	Other Expenses OtherExpenses	800997000	USD
CY2019	acgl	Underwriting Income Loss Segment UnderwritingIncomeLossSegment	1035965000	USD
CY2019	us-gaap	Investment Income Net InvestmentIncomeNet	627738000	USD
CY2019	us-gaap	Marketable Securities Gain Loss Excluding Other Than Temporary Impairments MarketableSecuritiesGainLossExcludingOtherThanTemporaryImpairments	363198000	USD
CY2019	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	123672000	USD
CY2019	acgl	Segment Other Cost And Expense Operating SegmentOtherCostAndExpenseOperating	65667000	USD
CY2019	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	14444000	USD
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	82104000	USD
CY2019	us-gaap	Interest Expense InterestExpense	120872000	USD
CY2019	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	-20609000	USD
CY2019	acgl	Income Loss From Continuing Operations Before Earnings From Affiliates Income Taxes Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeEarningsFromAffiliatesIncomeTaxesNoncontrollingInterest	1846877000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	155810000	USD
CY2019	acgl	Income Loss From Operating Affiliates Equity Method IncomeLossFromOperatingAffiliatesEquityMethod	2233000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	1693300000	USD
CY2019	us-gaap	Net Income Loss Attributable To Redeemable Noncontrolling Interest NetIncomeLossAttributableToRedeemableNoncontrollingInterest	16909000	USD
CY2019	us-gaap	Net Income Loss Attributable To Nonredeemable Noncontrolling Interest NetIncomeLossAttributableToNonredeemableNoncontrollingInterest	40072000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	1636319000	USD
CY2019	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	41612000	USD
CY2019	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	1594707000	USD
CY2019	us-gaap	Loss Ratio LossRatio	0.542
CY2019	acgl	Acquisition Expense Ratio Percentage AcquisitionExpenseRatioPercentage	0.145
CY2019	acgl	Other Operating Expense Ratio Percentage OtherOperatingExpenseRatioPercentage	0.138
CY2019	acgl	Combined Ratio Percentage CombinedRatioPercentage	0.825
CY2019Q4	us-gaap	Intangible Assets Net Including Goodwill IntangibleAssetsNetIncludingGoodwill	738083000	USD
CY2019Q4	acgl	Investable Assets InvestableAssets	24990265000	USD
CY2019Q4	us-gaap	Assets Assets	37885361000	USD
CY2019Q4	us-gaap	Liabilities Liabilities	25569809000	USD
CY2021	us-gaap	Schedule Of Liability For Unpaid Claims And Claims Adjustment Expense ScheduleOfLiabilityForUnpaidClaimsAndClaimsAdjustmentExpense	<div style="margin-bottom:10pt;margin-top:6pt;text-align:justify"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">The following table represents an analysis of losses and loss adjustment expenses and a reconciliation of the beginning and ending reserve for losses and loss adjustment expenses:</span></div><div style="margin-bottom:10pt;margin-top:5pt;text-align:justify"><table style="border-collapse:collapse;display:inline-table;margin-bottom:5pt;vertical-align:text-bottom;width:100.000%"><tr><td style="width:1.0%"/><td style="width:61.034%"/><td style="width:0.1%"/><td style="width:1.0%"/><td style="width:11.034%"/><td style="width:0.1%"/><td style="width:0.1%"/><td style="width:0.530%"/><td style="width:0.1%"/><td style="width:1.0%"/><td style="width:11.034%"/><td style="width:0.1%"/><td style="width:0.1%"/><td style="width:0.530%"/><td style="width:0.1%"/><td style="width:1.0%"/><td style="width:11.038%"/><td style="width:0.1%"/></tr><tr><td colspan="3" style="padding:0 1pt"/><td colspan="15" style="padding:2px 1pt;text-align:left;vertical-align:bottom"><div style="padding-left:4.5pt;padding-right:4.5pt;text-align:center"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:7.5pt;font-weight:700;line-height:100%">Year Ended December 31,</span></div></td></tr><tr><td colspan="3" style="padding:0 1pt"/><td colspan="3" style="border-top:1pt solid #000000;padding:2px 3.25pt;text-align:center;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:7.5pt;font-weight:700;line-height:100%">2021</span></td><td colspan="3" style="border-top:1pt solid #000000;padding:0 1pt"/><td colspan="3" style="border-top:1pt solid #000000;padding:2px 3.25pt;text-align:center;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:7.5pt;font-weight:700;line-height:100%">2020</span></td><td colspan="3" style="border-top:1pt solid #000000;padding:0 1pt"/><td colspan="3" style="border-top:1pt solid #000000;padding:2px 3.25pt;text-align:center;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:7.5pt;font-weight:700;line-height:100%">2019</span></td></tr><tr><td colspan="3" style="background-color:#cceeff;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Reserve for losses and loss adjustment expenses at beginning of year</span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">$</span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">16,513,929 </span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">$</span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">13,891,842 </span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">$</span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">11,853,297 </span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#ffffff;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Unpaid losses and loss adjustment expenses recoverable</span></td><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">4,314,855 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">4,082,650 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">2,814,291 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#cceeff;padding:2px 1pt 2px 7.75pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Net reserve for losses and loss adjustment expenses at beginning of year</span></td><td colspan="2" style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">12,199,074 </span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="2" style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">9,809,192 </span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="2" style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">9,039,006 </span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr style="height:11pt"><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/></tr><tr><td colspan="3" style="background-color:#cceeff;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Net incurred losses and loss adjustment expenses relating to losses occurring in:</span></td><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/></tr><tr><td colspan="3" style="background-color:#ffffff;padding:2px 1pt 2px 7.75pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Current year</span></td><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">4,940,987 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">4,851,051 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">3,297,037 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#cceeff;padding:2px 1pt 2px 7.75pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Prior years</span></td><td colspan="2" style="background-color:#cceeff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(356,184)</span></td><td style="background-color:#cceeff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="2" style="background-color:#cceeff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(161,452)</span></td><td style="background-color:#cceeff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="2" style="background-color:#cceeff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(163,585)</span></td><td style="background-color:#cceeff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#ffffff;padding:2px 1pt 2px 12.25pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Total net incurred losses and loss adjustment expenses</span></td><td colspan="2" style="background-color:#ffffff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">4,584,803 </span></td><td style="background-color:#ffffff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">4,689,599 </span></td><td style="background-color:#ffffff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">3,133,452 </span></td><td style="background-color:#ffffff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr style="height:11pt"><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/></tr><tr><td colspan="3" style="background-color:#ffffff;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Net losses and loss adjustment expense reserves of acquired business (1)</span></td><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">104,176 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">— </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">209,486 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr style="height:11pt"><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/></tr><tr><td colspan="3" style="background-color:#ffffff;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Retroactive reinsurance transactions (2)</span></td><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(444,147)</span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">182,210 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(225,500)</span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr style="height:11pt"><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/></tr><tr><td colspan="3" style="background-color:#ffffff;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Impact of deconsolidation of Somers (3)</span></td><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(1,460,611)</span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">— </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">— </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr style="height:11pt"><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/></tr><tr><td colspan="3" style="background-color:#ffffff;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Foreign exchange (gains) losses and other</span></td><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">1,181 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">179,190 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">36,003 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr style="height:11pt"><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/></tr><tr><td colspan="3" style="background-color:#ffffff;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Net paid losses and loss adjustment expenses relating to losses occurring in:</span></td><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/></tr><tr><td colspan="3" style="background-color:#cceeff;padding:2px 1pt 2px 7.75pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Current year</span></td><td colspan="2" style="background-color:#cceeff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(734,846)</span></td><td style="background-color:#cceeff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="2" style="background-color:#cceeff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(661,529)</span></td><td style="background-color:#cceeff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="2" style="background-color:#cceeff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(621,202)</span></td><td style="background-color:#cceeff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#ffffff;padding:2px 1pt 2px 7.75pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Prior years</span></td><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(2,091,705)</span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(1,999,588)</span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(1,762,053)</span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#cceeff;padding:2px 1pt 2px 12.25pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Total net paid losses and loss adjustment expenses</span></td><td colspan="2" style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(2,826,551)</span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="2" style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(2,661,117)</span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="2" style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">(2,383,255)</span></td><td style="background-color:#cceeff;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr style="height:11pt"><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/></tr><tr><td colspan="3" style="background-color:#cceeff;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Net reserve for losses and loss adjustment expenses at end of year</span></td><td colspan="2" style="background-color:#cceeff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">12,157,925 </span></td><td style="background-color:#cceeff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="2" style="background-color:#cceeff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">12,199,074 </span></td><td style="background-color:#cceeff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td colspan="2" style="background-color:#cceeff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">9,809,192 </span></td><td style="background-color:#cceeff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#ffffff;padding:2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Unpaid losses and loss adjustment expenses recoverable</span></td><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">5,599,231 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">4,314,855 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#ffffff;padding:0 1pt"/><td colspan="2" style="background-color:#ffffff;padding:2px 0 2px 1pt;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">4,082,650 </span></td><td style="background-color:#ffffff;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr><tr><td colspan="3" style="background-color:#cceeff;padding:2px 1pt 2px 7.75pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">Reserve for losses and loss adjustment expenses at end of year</span></td><td style="background-color:#cceeff;border-bottom:2pt solid #000000;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">$</span></td><td style="background-color:#cceeff;border-bottom:2pt solid #000000;border-top:1pt solid #000000;padding:2px 0;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">17,757,156 </span></td><td style="background-color:#cceeff;border-bottom:2pt solid #000000;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td style="background-color:#cceeff;border-bottom:2pt solid #000000;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">$</span></td><td style="background-color:#cceeff;border-bottom:2pt solid #000000;border-top:1pt solid #000000;padding:2px 0;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">16,513,929 </span></td><td style="background-color:#cceeff;border-bottom:2pt solid #000000;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/><td colspan="3" style="background-color:#cceeff;padding:0 1pt"/><td style="background-color:#cceeff;border-bottom:2pt solid #000000;border-top:1pt solid #000000;padding:2px 0 2px 1pt;text-align:left;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">$</span></td><td style="background-color:#cceeff;border-bottom:2pt solid #000000;border-top:1pt solid #000000;padding:2px 0;text-align:right;vertical-align:bottom"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:100%">13,891,842 </span></td><td style="background-color:#cceeff;border-bottom:2pt solid #000000;border-top:1pt solid #000000;padding:2px 1pt 2px 0;text-align:right;vertical-align:bottom"/></tr></table></div><div style="padding-left:22.5pt;text-indent:-22.5pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:9pt;font-weight:400;line-height:120%">(</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:120%">1) Represents activity related to the Company’s acquisitions in the 2021 and the 2019 period. See </span><span style="color:#0000ff;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:120%;text-decoration:underline"><a href="#i9aa6868b2b724c09bc653e55fc47166e_148" style="color:#0000ff;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:120%;text-decoration:underline">Note 2</a></span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:120%">.</span></div><div style="padding-left:22.5pt;text-indent:-22.5pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:120%">(2) See ‘Retroactive Reinsurance Transactions’ section.</span></div><div style="padding-left:22.5pt;text-indent:-22.5pt"><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:120%">(3) See <a href="#i9aa6868b2b724c09bc653e55fc47166e_178" style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:8pt;font-weight:400;line-height:120%;text-decoration:none">note 12</a>.</span></div>
CY2020Q4	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	16513929000	USD
CY2019Q4	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	13891842000	USD
CY2018Q4	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	11853297000	USD
CY2020Q4	us-gaap	Reinsurance Recoverable For Unpaid Claims And Claims Adjustments ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments	4314855000	USD
CY2019Q4	us-gaap	Reinsurance Recoverable For Unpaid Claims And Claims Adjustments ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments	4082650000	USD
CY2018Q4	us-gaap	Reinsurance Recoverable For Unpaid Claims And Claims Adjustments ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments	2814291000	USD
CY2020Q4	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Net LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	12199074000	USD
CY2019Q4	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Net LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	9809192000	USD
CY2018Q4	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Net LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	9039006000	USD
CY2021	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Current Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense	4940987000	USD
CY2020	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Current Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense	4851051000	USD
CY2019	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Current Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense	3297037000	USD
CY2021	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Prior Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense	-356184000	USD
CY2020	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Prior Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense	-161452000	USD
CY2019	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Prior Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense	-163585000	USD
CY2021	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1	4584803000	USD
CY2020	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1	4689599000	USD
CY2019	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1	3133452000	USD
CY2021	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Business Acquisitions LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseBusinessAcquisitions	104176000	USD
CY2020	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Business Acquisitions LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseBusinessAcquisitions	0	USD
CY2019	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Business Acquisitions LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseBusinessAcquisitions	209486000	USD
CY2021	acgl	Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims Retroactive Reinsurance LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsRetroactiveReinsurance	444147000	USD
CY2020	acgl	Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims Retroactive Reinsurance LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsRetroactiveReinsurance	-182210000	USD
CY2019	acgl	Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims Retroactive Reinsurance LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsRetroactiveReinsurance	225500000	USD
CY2021	acgl	Liability For Unpaid Claims And Claims Adjustment Expense Impact Of Deconsolidation LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseImpactOfDeconsolidation	1460611000	USD
CY2020	acgl	Liability For Unpaid Claims And Claims Adjustment Expense Impact Of Deconsolidation LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseImpactOfDeconsolidation	0	USD
CY2019	acgl	Liability For Unpaid Claims And Claims Adjustment Expense Impact Of Deconsolidation LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseImpactOfDeconsolidation	0	USD
CY2021	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Foreign Currency Translation Gain Loss LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseForeignCurrencyTranslationGainLoss	1181000	USD
CY2020	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Foreign Currency Translation Gain Loss LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseForeignCurrencyTranslationGainLoss	179190000	USD
CY2019	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Foreign Currency Translation Gain Loss LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseForeignCurrencyTranslationGainLoss	36003000	USD
CY2021	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Claims Paid Current Year1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1	734846000	USD
CY2020	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Claims Paid Current Year1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1	661529000	USD
CY2019	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Claims Paid Current Year1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1	621202000	USD
CY2021	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Claims Paid Prior Years1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1	2091705000	USD
CY2020	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Claims Paid Prior Years1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1	1999588000	USD
CY2019	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Claims Paid Prior Years1 LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1	1762053000	USD
CY2021	us-gaap	Payments For Losses And Loss Adjustment Expense PaymentsForLossesAndLossAdjustmentExpense	2826551000	USD
CY2020	us-gaap	Payments For Losses And Loss Adjustment Expense PaymentsForLossesAndLossAdjustmentExpense	2661117000	USD
CY2019	us-gaap	Payments For Losses And Loss Adjustment Expense PaymentsForLossesAndLossAdjustmentExpense	2383255000	USD
CY2021Q4	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Net LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	12157925000	USD
CY2020Q4	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Net LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	12199074000	USD
CY2019Q4	us-gaap	Liability For Unpaid Claims And Claims Adjustment Expense Net LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	9809192000	USD
CY2021Q4	us-gaap	Reinsurance Recoverable For Unpaid Claims And Claims Adjustments ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments	5599231000	USD
CY2020Q4	us-gaap	Reinsurance Recoverable For Unpaid Claims And Claims Adjustments ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments	4314855000	USD
CY2019Q4	us-gaap	Reinsurance Recoverable For Unpaid Claims And Claims Adjustments ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments	4082650000	USD
CY2021Q4	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	17757156000	USD
CY2020Q4	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	16513929000	USD
CY2019Q4	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	13891842000	USD
CY2021	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Prior Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense	-356200000	USD
CY2020	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Prior Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense	-161500000	USD
CY2019	us-gaap	Supplemental Information For Property Casualty Insurance Underwriters Prior Year Claims And Claims Adjustment Expense SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense	-163600000	USD
CY2021Q4	us-gaap	Shortduration Insurance Contracts Liability For Unpaid Claims And Allocated Claim Adjustment Expense Net ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndAllocatedClaimAdjustmentExpenseNet	11886330000	USD
CY2021Q4	us-gaap	Shortduration Insurance Contracts Liability For Unpaid Claims And Claim Adjustment Expense Other Reconciling Item ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndClaimAdjustmentExpenseOtherReconcilingItem	76240000	USD
CY2021Q4	us-gaap	Shortduration Insurance Contracts Discounted Liabilities Aggregate Discount ShortdurationInsuranceContractsDiscountedLiabilitiesAggregateDiscount	55575000	USD
CY2021Q4	us-gaap	Shortduration Insurance Contracts Liability For Unpaid Claims And Claims Adjustment Expense Accumulated Unallocated Claim Adjustment Expense ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseAccumulatedUnallocatedClaimAdjustmentExpense	225033000	USD
CY2021Q4	us-gaap	Shortduration Insurance Contracts Liability For Unpaid Claims And Claim Adjustment Expense Aggregate Reconciling Items ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndClaimAdjustmentExpenseAggregateReconcilingItems	245698000	USD
CY2021Q4	us-gaap	Liability For Claims And Claims Adjustment Expense LiabilityForClaimsAndClaimsAdjustmentExpense	17757156000	USD
CY2020Q4	us-gaap	Premiums Receivable At Carrying Value PremiumsReceivableAtCarryingValue	2064586000	USD
CY2020Q4	us-gaap	Premiums Receivable Allowance For Doubtful Accounts PremiumsReceivableAllowanceForDoubtfulAccounts	37781000	USD
CY2021	us-gaap	Premium Receivable Credit Loss Expense Reversal PremiumReceivableCreditLossExpenseReversal	2177000	USD
CY2021Q4	us-gaap	Premiums Receivable At Carrying Value PremiumsReceivableAtCarryingValue	2633280000	USD
CY2021Q4	us-gaap	Premiums Receivable Allowance For Doubtful Accounts PremiumsReceivableAllowanceForDoubtfulAccounts	39958000	USD
CY2019Q4	us-gaap	Premiums Receivable At Carrying Value PremiumsReceivableAtCarryingValue	1778717000	USD
CY2019Q4	us-gaap	Premiums Receivable Allowance For Doubtful Accounts PremiumsReceivableAllowanceForDoubtfulAccounts	21003000	USD
CY2020	acgl	Premiums Receivable Change In Method Credit Loss Expense Reversal PremiumsReceivableChangeInMethodCreditLossExpenseReversal	6539000	USD
CY2020	us-gaap	Premium Receivable Credit Loss Expense Reversal PremiumReceivableCreditLossExpenseReversal	10239000	USD
CY2020Q4	us-gaap	Premiums Receivable At Carrying Value PremiumsReceivableAtCarryingValue	2064586000	USD
CY2020Q4	us-gaap	Premiums Receivable Allowance For Doubtful Accounts PremiumsReceivableAllowanceForDoubtfulAccounts	37781000	USD
CY2021	us-gaap	Premiums Receivable Allowance For Doubtful Accounts Write Offs Against Allowance PremiumsReceivableAllowanceForDoubtfulAccountsWriteOffsAgainstAllowance	3800000	USD
CY2020	us-gaap	Premiums Receivable Allowance For Doubtful Accounts Write Offs Against Allowance PremiumsReceivableAllowanceForDoubtfulAccountsWriteOffsAgainstAllowance	2800000	USD
CY2020Q4	us-gaap	Reinsurance Recoverables On Paid And Unpaid Losses ReinsuranceRecoverablesOnPaidAndUnpaidLosses	4500802000	USD
CY2020Q4	us-gaap	Reinsurance Recoverables Allowance ReinsuranceRecoverablesAllowance	11636000	USD
CY2021	us-gaap	Reinsurance Recoverable Credit Loss Expense Reversal ReinsuranceRecoverableCreditLossExpenseReversal	1594000	USD
CY2021Q4	us-gaap	Reinsurance Recoverables On Paid And Unpaid Losses ReinsuranceRecoverablesOnPaidAndUnpaidLosses	5880735000	USD
CY2021Q4	us-gaap	Reinsurance Recoverables Allowance ReinsuranceRecoverablesAllowance	13230000	USD
CY2019Q4	us-gaap	Reinsurance Recoverables On Paid And Unpaid Losses ReinsuranceRecoverablesOnPaidAndUnpaidLosses	4346816000	USD
CY2019Q4	us-gaap	Reinsurance Recoverables Allowance ReinsuranceRecoverablesAllowance	1364000	USD
CY2020	us-gaap	Reinsurance Recoverable Change In Method Credit Loss Expense Reversal ReinsuranceRecoverableChangeInMethodCreditLossExpenseReversal	12010000	USD
CY2020	us-gaap	Reinsurance Recoverable Credit Loss Expense Reversal ReinsuranceRecoverableCreditLossExpenseReversal	-1738000	USD
CY2020Q4	us-gaap	Reinsurance Recoverables On Paid And Unpaid Losses ReinsuranceRecoverablesOnPaidAndUnpaidLosses	4500802000	USD
CY2020Q4	us-gaap	Reinsurance Recoverables Allowance ReinsuranceRecoverablesAllowance	11636000	USD
CY2019Q4	acgl	Contractholder Receivables Allowance For Credit Loss ContractholderReceivablesAllowanceForCreditLoss	0	USD
CY2021Q4	us-gaap	Reinsurance Recoverables On Paid And Unpaid Losses ReinsuranceRecoverablesOnPaidAndUnpaidLosses	5880735000	USD
CY2020Q4	us-gaap	Reinsurance Recoverables On Paid And Unpaid Losses ReinsuranceRecoverablesOnPaidAndUnpaidLosses	4500802000	USD
CY2020Q4	acgl	Contractholder Deductibles Receivable ContractholderDeductiblesReceivable	1986924000	USD
CY2020Q4	acgl	Contractholder Receivables Allowance For Credit Loss ContractholderReceivablesAllowanceForCreditLoss	8638000	USD
CY2021	acgl	Contractholder Receivables Credit Loss Expense Reversal ContractholderReceivablesCreditLossExpenseReversal	-5201000	USD
CY2021Q4	acgl	Contractholder Deductibles Receivable ContractholderDeductiblesReceivable	1828691000	USD
CY2021Q4	acgl	Contractholder Receivables Allowance For Credit Loss ContractholderReceivablesAllowanceForCreditLoss	3437000	USD
CY2019Q4	acgl	Contractholder Deductibles Receivable ContractholderDeductiblesReceivable	2119460000	USD
CY2020	acgl	Contractholder Receivable Change In Method Credit Loss Expense Reversal ContractholderReceivableChangeInMethodCreditLossExpenseReversal	6663000	USD
CY2020	acgl	Contractholder Receivables Credit Loss Expense Reversal ContractholderReceivablesCreditLossExpenseReversal	1975000	USD
CY2020Q4	acgl	Contractholder Deductibles Receivable ContractholderDeductiblesReceivable	1986924000	USD
CY2020Q4	acgl	Contractholder Receivables Allowance For Credit Loss ContractholderReceivablesAllowanceForCreditLoss	8638000	USD
CY2021	us-gaap	Direct Premiums Written DirectPremiumsWritten	7706832000	USD
CY2020	us-gaap	Direct Premiums Written DirectPremiumsWritten	6553910000	USD
CY2019	us-gaap	Direct Premiums Written DirectPremiumsWritten	5681523000	USD
CY2021	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	5045655000	USD
CY2020	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	3534158000	USD
CY2019	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	2457437000	USD
CY2021	us-gaap	Ceded Premiums Written CededPremiumsWritten	3734150000	USD
CY2020	us-gaap	Ceded Premiums Written CededPremiumsWritten	2650352000	USD
CY2019	us-gaap	Ceded Premiums Written CededPremiumsWritten	2099893000	USD
CY2021	us-gaap	Premiums Written Net PremiumsWrittenNet	9018337000	USD
CY2020	us-gaap	Premiums Written Net PremiumsWrittenNet	7437716000	USD
CY2019	us-gaap	Premiums Written Net PremiumsWrittenNet	6039067000	USD
CY2021	us-gaap	Direct Premiums Earned DirectPremiumsEarned	7149794000	USD
CY2020	us-gaap	Direct Premiums Earned DirectPremiumsEarned	6361451000	USD
CY2019	us-gaap	Direct Premiums Earned DirectPremiumsEarned	5447829000	USD
CY2021	us-gaap	Assumed Premiums Earned AssumedPremiumsEarned	4333873000	USD
CY2020	us-gaap	Assumed Premiums Earned AssumedPremiumsEarned	3213873000	USD
CY2019	us-gaap	Assumed Premiums Earned AssumedPremiumsEarned	2337950000	USD
CY2021	us-gaap	Ceded Premiums Earned CededPremiumsEarned	3401369000	USD
CY2020	us-gaap	Ceded Premiums Earned CededPremiumsEarned	2583389000	USD
CY2019	us-gaap	Ceded Premiums Earned CededPremiumsEarned	1999281000	USD
CY2021	us-gaap	Premiums Earned Net PremiumsEarnedNet	8082298000	USD
CY2020	us-gaap	Premiums Earned Net PremiumsEarnedNet	6991935000	USD
CY2019	us-gaap	Premiums Earned Net PremiumsEarnedNet	5786498000	USD
CY2021	us-gaap	Policyholder Benefits And Claims Incurred Gross PolicyholderBenefitsAndClaimsIncurredGross	4266758000	USD
CY2020	us-gaap	Policyholder Benefits And Claims Incurred Gross PolicyholderBenefitsAndClaimsIncurredGross	4392392000	USD
CY2019	us-gaap	Policyholder Benefits And Claims Incurred Gross PolicyholderBenefitsAndClaimsIncurredGross	2953072000	USD
CY2021	us-gaap	Reinsurance Effect On Claims And Benefits Incurred Amount Assumed ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountAssumed	2826820000	USD
CY2020	us-gaap	Reinsurance Effect On Claims And Benefits Incurred Amount Assumed ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountAssumed	2204323000	USD
CY2019	us-gaap	Reinsurance Effect On Claims And Benefits Incurred Amount Assumed ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountAssumed	1602528000	USD
CY2021	us-gaap	Reinsurance Effect On Claims And Benefits Incurred Amount Ceded ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded	2508775000	USD
CY2020	us-gaap	Reinsurance Effect On Claims And Benefits Incurred Amount Ceded ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded	1907116000	USD
CY2019	us-gaap	Reinsurance Effect On Claims And Benefits Incurred Amount Ceded ReinsuranceEffectOnClaimsAndBenefitsIncurredAmountCeded	1422148000	USD
CY2021	us-gaap	Policyholder Benefits And Claims Incurred Net PolicyholderBenefitsAndClaimsIncurredNet	4584803000	USD
CY2020	us-gaap	Policyholder Benefits And Claims Incurred Net PolicyholderBenefitsAndClaimsIncurredNet	4689599000	USD
CY2019	us-gaap	Policyholder Benefits And Claims Incurred Net PolicyholderBenefitsAndClaimsIncurredNet	3133452000	USD
CY2021Q4	acgl	Available For Sale Investments Fair Value Fixed Maturities And Short Term AvailableForSaleInvestmentsFairValueFixedMaturitiesAndShortTerm	19732825000	USD
CY2021Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	198691000	USD
CY2021Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	171544000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss DebtSecuritiesAvailableForSaleAllowanceForCreditLoss	2883000	USD
CY2021Q4	acgl	Available For Sale Investments Cost Or Amortized Cost Fixed Maturities And Short Term AvailableForSaleInvestmentsCostOrAmortizedCostFixedMaturitiesAndShortTerm	19708561000	USD
CY2020Q4	acgl	Available For Sale Investments Fair Value Fixed Maturities And Short Term AvailableForSaleInvestmentsFairValueFixedMaturitiesAndShortTerm	20921530000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	657620000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	79654000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss DebtSecuritiesAvailableForSaleAllowanceForCreditLoss	2397000	USD
CY2020Q4	acgl	Available For Sale Investments Cost Or Amortized Cost Fixed Maturities And Short Term AvailableForSaleInvestmentsCostOrAmortizedCostFixedMaturitiesAndShortTerm	20345961000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	12238683000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	157279000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	297357000	USD
CY2021Q4	acgl	Available For Sale Securities Qualitative Disclosure Largest Single Loss AvailableForSaleSecuritiesQualitativeDisclosureLargestSingleLoss	1100000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	14265000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	12536040000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	171544000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	3788763000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	76067000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	70404000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	3587000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	3859167000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	79654000	USD
CY2021Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Number Of Positions DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions	4700	lots
CY2021Q4	acgl	Available For Sale Securities Qualitative Disclosure Number Of Positions AvailableForSaleSecuritiesQualitativeDisclosureNumberOfPositions	10240	lots
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Number Of Positions DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions	2320	lots
CY2020Q4	acgl	Available For Sale Securities Qualitative Disclosure Number Of Positions AvailableForSaleSecuritiesQualitativeDisclosureNumberOfPositions	11180	lots
CY2020Q4	acgl	Available For Sale Securities Qualitative Disclosure Largest Single Loss AvailableForSaleSecuritiesQualitativeDisclosureLargestSingleLoss	900000	USD
CY2020Q4	us-gaap	Obligation To Return Securities Received As Collateral ObligationToReturnSecuritiesReceivedAsCollateral	301089000	USD
CY2020Q4	us-gaap	Secured Borrowings Gross Difference Amount SecuredBorrowingsGrossDifferenceAmount	0	USD
CY2020Q4	us-gaap	Secured Borrowings Gross Including Not Subject To Master Netting Arrangement SecuredBorrowingsGrossIncludingNotSubjectToMasterNettingArrangement	301089000	USD
CY2021Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	1800000000	USD
CY2020Q4	us-gaap	Equity Securities Fv Ni EquitySecuritiesFvNi	1400000000	USD
CY2021	us-gaap	Investment Income Interest And Dividend InvestmentIncomeInterestAndDividend	477123000	USD
CY2020	us-gaap	Investment Income Interest And Dividend InvestmentIncomeInterestAndDividend	608823000	USD
CY2019	us-gaap	Investment Income Interest And Dividend InvestmentIncomeInterestAndDividend	716643000	USD
CY2021	us-gaap	Investment Income Investment Expense InvestmentIncomeInvestmentExpense	88005000	USD
CY2020	us-gaap	Investment Income Investment Expense InvestmentIncomeInvestmentExpense	89215000	USD
CY2019	us-gaap	Investment Income Investment Expense InvestmentIncomeInvestmentExpense	88905000	USD
CY2021	us-gaap	Investment Income Net InvestmentIncomeNet	389118000	USD
CY2020	us-gaap	Investment Income Net InvestmentIncomeNet	519608000	USD
CY2019	us-gaap	Investment Income Net InvestmentIncomeNet	627738000	USD
CY2021	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	313886000	USD
CY2020	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	595941000	USD
CY2019	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	235655000	USD
CY2021	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	156791000	USD
CY2020	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	117282000	USD
CY2019	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	104612000	USD
CY2021	us-gaap	Equity Securities Fv Ni Realized Gain Loss EquitySecuritiesFvNiRealizedGainLoss	122606000	USD
CY2020	us-gaap	Equity Securities Fv Ni Realized Gain Loss EquitySecuritiesFvNiRealizedGainLoss	26849000	USD
CY2019	us-gaap	Equity Securities Fv Ni Realized Gain Loss EquitySecuritiesFvNiRealizedGainLoss	11313000	USD
CY2021	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	48746000	USD
CY2020	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	102394000	USD
CY2019	us-gaap	Equity Securities Fv Ni Unrealized Gain Loss EquitySecuritiesFvNiUnrealizedGainLoss	97768000	USD
CY2021	us-gaap	Debt Securities Available For Sale Change In Present Value Expense Reversal DebtSecuritiesAvailableForSaleChangeInPresentValueExpenseReversal	2100000	USD
CY2020	us-gaap	Debt Securities Available For Sale Change In Present Value Expense Reversal DebtSecuritiesAvailableForSaleChangeInPresentValueExpenseReversal	3597000	USD
CY2019	us-gaap	Debt Securities Available For Sale Change In Present Value Expense Reversal DebtSecuritiesAvailableForSaleChangeInPresentValueExpenseReversal	0	USD
CY2021	acgl	Underwriting Related Allowance For Credit Losses Credit Loss Expense Reversal UnderwritingRelatedAllowanceForCreditLossesCreditLossExpenseReversal	-1062000	USD
CY2020	acgl	Underwriting Related Allowance For Credit Losses Credit Loss Expense Reversal UnderwritingRelatedAllowanceForCreditLossesCreditLossExpenseReversal	10007000	USD
CY2019	acgl	Underwriting Related Allowance For Credit Losses Credit Loss Expense Reversal UnderwritingRelatedAllowanceForCreditLossesCreditLossExpenseReversal	0	USD
CY2021	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss Writeoff DebtSecuritiesAvailableForSaleAllowanceForCreditLossWriteoff	0	USD
CY2020	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss Writeoff DebtSecuritiesAvailableForSaleAllowanceForCreditLossWriteoff	533000	USD
CY2019	us-gaap	Other Than Temporary Impairment Loss Debt Securities Available For Sale Recognized In Earnings OtherThanTemporaryImpairmentLossDebtSecuritiesAvailableForSaleRecognizedInEarnings	3165000	USD
CY2021	us-gaap	Derivative Gain Loss On Derivative Net DerivativeGainLossOnDerivativeNet	-32390000	USD
CY2020	us-gaap	Derivative Gain Loss On Derivative Net DerivativeGainLossOnDerivativeNet	179675000	USD
CY2019	us-gaap	Derivative Gain Loss On Derivative Net DerivativeGainLossOnDerivativeNet	119741000	USD
CY2021	us-gaap	Gain Loss On Sale Of Other Investments GainLossOnSaleOfOtherInvestments	-53537000	USD
CY2020	us-gaap	Gain Loss On Sale Of Other Investments GainLossOnSaleOfOtherInvestments	3575000	USD
CY2019	us-gaap	Gain Loss On Sale Of Other Investments GainLossOnSaleOfOtherInvestments	-19348000	USD
CY2021	us-gaap	Marketable Securities Gain Loss Excluding Other Than Temporary Impairments MarketableSecuritiesGainLossExcludingOtherThanTemporaryImpairments	379845000	USD
CY2020	us-gaap	Marketable Securities Gain Loss Excluding Other Than Temporary Impairments MarketableSecuritiesGainLossExcludingOtherThanTemporaryImpairments	823460000	USD
CY2019	us-gaap	Marketable Securities Gain Loss Excluding Other Than Temporary Impairments MarketableSecuritiesGainLossExcludingOtherThanTemporaryImpairments	363198000	USD
CY2021Q4	us-gaap	Variable Interest Entity Entity Maximum Loss Exposure Amount VariableInterestEntityEntityMaximumLossExposureAmount	3248206000	USD
CY2021Q4	acgl	Investments Accounted For Using Fair Value Option InvestmentsAccountedForUsingFairValueOption	1973550000	USD
CY2020Q4	acgl	Investments Accounted For Using Fair Value Option InvestmentsAccountedForUsingFairValueOption	3824796000	USD
CY2021Q4	us-gaap	Other Investments And Securities At Cost OtherInvestmentsAndSecuritiesAtCost	0	USD
CY2020Q4	us-gaap	Other Investments And Securities At Cost OtherInvestmentsAndSecuritiesAtCost	500000000	USD
CY2021Q4	us-gaap	Other Investments OtherInvestments	1973550000	USD
CY2020Q4	us-gaap	Other Investments OtherInvestments	4324796000	USD
CY2021Q4	us-gaap	Equity Method Investments EquityMethodInvestments	3077611000	USD
CY2020Q4	us-gaap	Equity Method Investments EquityMethodInvestments	2047889000	USD
CY2021	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	366400000	USD
CY2020	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	146700000	USD
CY2019	us-gaap	Income Loss From Equity Method Investments IncomeLossFromEquityMethodInvestments	123700000	USD
CY2021	acgl	Income Loss From Operating Affiliates Equity Method IncomeLossFromOperatingAffiliatesEquityMethod	264700000	USD
CY2020Q4	us-gaap	Variable Interest Entity Entity Maximum Loss Exposure Amount VariableInterestEntityEntityMaximumLossExposureAmount	2232609000	USD
CY2020	acgl	Income Loss From Operating Affiliates Equity Method IncomeLossFromOperatingAffiliatesEquityMethod	16800000	USD
CY2019	acgl	Income Loss From Operating Affiliates Equity Method IncomeLossFromOperatingAffiliatesEquityMethod	2200000	USD
CY2021Q4	acgl	Restricted Assets RestrictedAssets	8249732000	USD
CY2020Q4	acgl	Restricted Assets RestrictedAssets	8733309000	USD
CY2021Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	858668000	USD
CY2020Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	906448000	USD
CY2019Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	726230000	USD
CY2021Q4	us-gaap	Restricted Cash And Cash Equivalents RestrictedCashAndCashEquivalents	456103000	USD
CY2020Q4	us-gaap	Restricted Cash And Cash Equivalents RestrictedCashAndCashEquivalents	384096000	USD
CY2019Q4	us-gaap	Restricted Cash And Cash Equivalents RestrictedCashAndCashEquivalents	177468000	USD
CY2021Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	1314771000	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	1290544000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	903698000	USD
CY2021Q4	acgl	Total Assets And Liabilities Measured At Fair Value TotalAssetsAndLiabilitiesMeasuredAtFairValue	23800000000	USD
CY2021Q4	acgl	Total Assets And Liabilities Measured At Fair Value Priced Using Non Binding Broker Quotes TotalAssetsAndLiabilitiesMeasuredAtFairValuePricedUsingNonBindingBrokerQuotes	7700000	USD
CY2021Q4	acgl	Percentage Of Total Assets And Liabilities Measured At Fair Value Priced Using Non Binding Broker Quotes PercentageOfTotalAssetsAndLiabilitiesMeasuredAtFairValuePricedUsingNonBindingBrokerQuotes	0.000
CY2020Q4	acgl	Total Assets And Liabilities Measured At Fair Value TotalAssetsAndLiabilitiesMeasuredAtFairValue	26500000000	USD
CY2020Q4	acgl	Total Assets And Liabilities Measured At Fair Value Priced Using Non Binding Broker Quotes TotalAssetsAndLiabilitiesMeasuredAtFairValuePricedUsingNonBindingBrokerQuotes	150100000	USD
CY2020Q4	acgl	Percentage Of Total Assets And Liabilities Measured At Fair Value Priced Using Non Binding Broker Quotes PercentageOfTotalAssetsAndLiabilitiesMeasuredAtFairValuePricedUsingNonBindingBrokerQuotes	0.006
CY2021Q4	us-gaap	Derivative Fair Value Of Derivative Asset Amount Not Offset Against Collateral DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral	122300000	USD
CY2021Q4	us-gaap	Derivative Fair Value Of Derivative Liability Amount Not Offset Against Collateral DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral	53900000	USD
CY2020Q4	us-gaap	Derivative Fair Value Of Derivative Asset Amount Not Offset Against Collateral DerivativeFairValueOfDerivativeAssetAmountNotOffsetAgainstCollateral	138800000	USD
CY2020Q4	us-gaap	Derivative Fair Value Of Derivative Liability Amount Not Offset Against Collateral DerivativeFairValueOfDerivativeLiabilityAmountNotOffsetAgainstCollateral	93000000	USD
CY2020Q4	us-gaap	Redeemable Noncontrolling Interest Equity Fair Value RedeemableNoncontrollingInterestEquityFairValue	58548000	USD
CY2019Q4	us-gaap	Redeemable Noncontrolling Interest Equity Fair Value RedeemableNoncontrollingInterestEquityFairValue	55404000	USD
CY2018Q4	us-gaap	Redeemable Noncontrolling Interest Equity Fair Value RedeemableNoncontrollingInterestEquityFairValue	206292000	USD
CY2021	acgl	Redeemable Noncontrolling Interest Decrease From Deconsolidation RedeemableNoncontrollingInterestDecreaseFromDeconsolidation	48919000	USD
CY2020	acgl	Redeemable Noncontrolling Interest Decrease From Deconsolidation RedeemableNoncontrollingInterestDecreaseFromDeconsolidation	0	USD
CY2019	acgl	Redeemable Noncontrolling Interest Decrease From Deconsolidation RedeemableNoncontrollingInterestDecreaseFromDeconsolidation	0	USD
CY2021	acgl	Redeemable Noncontrolling Interest Increasefrom Subsidiary Equity Issuance RedeemableNoncontrollingInterestIncreasefromSubsidiaryEquityIssuance	0	USD
CY2020	acgl	Redeemable Noncontrolling Interest Increasefrom Subsidiary Equity Issuance RedeemableNoncontrollingInterestIncreasefromSubsidiaryEquityIssuance	0	USD
CY2019	acgl	Redeemable Noncontrolling Interest Increasefrom Subsidiary Equity Issuance RedeemableNoncontrollingInterestIncreasefromSubsidiaryEquityIssuance	-157709000	USD
CY2021	acgl	Redeemable Noncontrolling Interest Accretionof Issuance Costs RedeemableNoncontrollingInterestAccretionofIssuanceCosts	0	USD
CY2020	acgl	Redeemable Noncontrolling Interest Accretionof Issuance Costs RedeemableNoncontrollingInterestAccretionofIssuanceCosts	93000	USD
CY2019	acgl	Redeemable Noncontrolling Interest Accretionof Issuance Costs RedeemableNoncontrollingInterestAccretionofIssuanceCosts	244000	USD
CY2021	acgl	Noncontrolling Interest Period Increase Decrease Other NoncontrollingInterestPeriodIncreaseDecreaseOther	-396000	USD
CY2020	acgl	Noncontrolling Interest Period Increase Decrease Other NoncontrollingInterestPeriodIncreaseDecreaseOther	3051000	USD
CY2019	acgl	Noncontrolling Interest Period Increase Decrease Other NoncontrollingInterestPeriodIncreaseDecreaseOther	6577000	USD
CY2021Q4	us-gaap	Redeemable Noncontrolling Interest Equity Fair Value RedeemableNoncontrollingInterestEquityFairValue	9233000	USD
CY2020Q4	us-gaap	Redeemable Noncontrolling Interest Equity Fair Value RedeemableNoncontrollingInterestEquityFairValue	58548000	USD
CY2019Q4	us-gaap	Redeemable Noncontrolling Interest Equity Fair Value RedeemableNoncontrollingInterestEquityFairValue	55404000	USD
CY2021	us-gaap	Net Income Loss Attributable To Nonredeemable Noncontrolling Interest NetIncomeLossAttributableToNonredeemableNoncontrollingInterest	78314000	USD
CY2021	us-gaap	Net Income Loss Attributable To Nonredeemable Noncontrolling Interest NetIncomeLossAttributableToNonredeemableNoncontrollingInterest	78314000	USD
CY2020	us-gaap	Net Income Loss Attributable To Nonredeemable Noncontrolling Interest NetIncomeLossAttributableToNonredeemableNoncontrollingInterest	53076000	USD
CY2020	us-gaap	Net Income Loss Attributable To Nonredeemable Noncontrolling Interest NetIncomeLossAttributableToNonredeemableNoncontrollingInterest	53076000	USD
CY2020	us-gaap	Net Income Loss Attributable To Nonredeemable Noncontrolling Interest NetIncomeLossAttributableToNonredeemableNoncontrollingInterest	53076000	USD
CY2019	us-gaap	Net Income Loss Attributable To Nonredeemable Noncontrolling Interest NetIncomeLossAttributableToNonredeemableNoncontrollingInterest	40072000	USD
CY2019	us-gaap	Net Income Loss Attributable To Nonredeemable Noncontrolling Interest NetIncomeLossAttributableToNonredeemableNoncontrollingInterest	40072000	USD
CY2021	us-gaap	Net Income Loss Attributable To Redeemable Noncontrolling Interest NetIncomeLossAttributableToRedeemableNoncontrollingInterest	4299000	USD
CY2020	us-gaap	Net Income Loss Attributable To Redeemable Noncontrolling Interest NetIncomeLossAttributableToRedeemableNoncontrollingInterest	7114000	USD
CY2019	us-gaap	Net Income Loss Attributable To Redeemable Noncontrolling Interest NetIncomeLossAttributableToRedeemableNoncontrollingInterest	16909000	USD
CY2021	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	82613000	USD
CY2020	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	60190000	USD
CY2019	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	56981000	USD
CY2020Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	488895000	USD
CY2021	us-gaap	Oci Before Reclassifications Net Of Tax Attributable To Parent OciBeforeReclassificationsNetOfTaxAttributableToParent	-437427000	USD
CY2021	us-gaap	Reclassification From Aoci Current Period Net Of Tax Attributable To Parent ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent	116068000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	-553495000	USD
CY2021Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-64600000	USD
CY2019Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	212091000	USD
CY2020	us-gaap	Oci Before Reclassifications Net Of Tax Attributable To Parent OciBeforeReclassificationsNetOfTaxAttributableToParent	702991000	USD
CY2020	us-gaap	Reclassification From Aoci Current Period Net Of Tax Attributable To Parent ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent	426187000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	276804000	USD
CY2020Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	488895000	USD
CY2018Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	-178720000	USD
CY2019	us-gaap	Oci Before Reclassifications Net Of Tax Attributable To Parent OciBeforeReclassificationsNetOfTaxAttributableToParent	509752000	USD
CY2019	us-gaap	Reclassification From Aoci Current Period Net Of Tax Attributable To Parent ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent	118941000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax Portion Attributable To Parent OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent	390811000	USD
CY2019Q4	us-gaap	Accumulated Other Comprehensive Income Loss Net Of Tax AccumulatedOtherComprehensiveIncomeLossNetOfTax	212091000	USD
CY2021	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	-406774000	USD
CY2021	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	-19845000	USD
CY2021	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	-386929000	USD
CY2021	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Before Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax	154996000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	38928000	USD
CY2021	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	116068000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Before Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax	-64423000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Foreign Currency Translation Adjustment Tax OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax	59000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	-64482000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	-626193000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	-58714000	USD
CY2021	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-567479000	USD
CY2020	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	754572000	USD
CY2020	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	75855000	USD
CY2020	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	678717000	USD
CY2020	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Before Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax	474529000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	48342000	USD
CY2020	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	426187000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Before Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax	33706000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Foreign Currency Translation Adjustment Tax OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax	370000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	33336000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	313749000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	27883000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	285866000	USD
CY2019	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodBeforeTax	562576000	USD
CY2019	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax	61805000	USD
CY2019	us-gaap	Other Comprehensive Income Unrealized Holding Gain Loss On Securities Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax	500771000	USD
CY2019	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Before Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax	127878000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesTax	8937000	USD
CY2019	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	118941000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Before Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentBeforeTax	18463000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Foreign Currency Translation Adjustment Tax OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax	353000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	18110000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	453161000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	53221000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	399940000	USD
CY2021	us-gaap	Profit Loss ProfitLoss	2239462000	USD
CY2020	us-gaap	Profit Loss ProfitLoss	1465711000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	1693300000	USD
CY2021	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	82613000	USD
CY2020	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	60190000	USD
CY2019	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	56981000	USD
CY2021	us-gaap	Net Income Loss NetIncomeLoss	2156849000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	1405521000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	1636319000	USD
CY2021	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	48343000	USD
CY2020	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	41612000	USD
CY2019	us-gaap	Preferred Stock Dividends Income Statement Impact PreferredStockDividendsIncomeStatementImpact	41612000	USD
CY2021	us-gaap	Preferred Stock Redemption Premium PreferredStockRedemptionPremium	15101000	USD
CY2020	us-gaap	Preferred Stock Redemption Premium PreferredStockRedemptionPremium	0	USD
CY2019	us-gaap	Preferred Stock Redemption Premium PreferredStockRedemptionPremium	0	USD
CY2021	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	2093405000	USD
CY2020	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	1363909000	USD
CY2019	us-gaap	Net Income Loss Available To Common Stockholders Basic NetIncomeLossAvailableToCommonStockholdersBasic	1594707000	USD
CY2021	us-gaap	Weighted Average Number Of Shares Issued Basic WeightedAverageNumberOfSharesIssuedBasic	391748715	shares
CY2020	us-gaap	Weighted Average Number Of Shares Issued Basic WeightedAverageNumberOfSharesIssuedBasic	403062179	shares
CY2019	us-gaap	Weighted Average Number Of Shares Issued Basic WeightedAverageNumberOfSharesIssuedBasic	401802815	shares
CY2021	us-gaap	Incremental Common Shares Attributable To Nonvested Shares With Forfeitable Dividends IncrementalCommonSharesAttributableToNonvestedSharesWithForfeitableDividends	1996524	shares
CY2020	us-gaap	Incremental Common Shares Attributable To Nonvested Shares With Forfeitable Dividends IncrementalCommonSharesAttributableToNonvestedSharesWithForfeitableDividends	1682309	shares
CY2019	us-gaap	Incremental Common Shares Attributable To Nonvested Shares With Forfeitable Dividends IncrementalCommonSharesAttributableToNonvestedSharesWithForfeitableDividends	1673770	shares
CY2021	us-gaap	Incremental Common Shares Attributable To Call Options And Warrants IncrementalCommonSharesAttributableToCallOptionsAndWarrants	6600697	shares
CY2020	us-gaap	Incremental Common Shares Attributable To Call Options And Warrants IncrementalCommonSharesAttributableToCallOptionsAndWarrants	5514967	shares
CY2019	us-gaap	Incremental Common Shares Attributable To Call Options And Warrants IncrementalCommonSharesAttributableToCallOptionsAndWarrants	8132893	shares
CY2021	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	400345936	shares
CY2020	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	410259455	shares
CY2019	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	411609478	shares
CY2021	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	5.34
CY2020	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.38
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.97
CY2021	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	5.23
CY2020	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.32
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.87
CY2021	us-gaap	Current Federal State And Local Tax Expense Benefit CurrentFederalStateAndLocalTaxExpenseBenefit	284274000	USD
CY2020	us-gaap	Current Federal State And Local Tax Expense Benefit CurrentFederalStateAndLocalTaxExpenseBenefit	181571000	USD
CY2019	us-gaap	Current Federal State And Local Tax Expense Benefit CurrentFederalStateAndLocalTaxExpenseBenefit	139407000	USD
CY2021	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	11259000	USD
CY2020	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	16091000	USD
CY2019	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	4954000	USD
CY2021	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	295533000	USD
CY2021	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	20978000	USD
CY2020	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	197662000	USD
CY2019	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	144361000	USD
CY2021	us-gaap	Deferred Federal State And Local Tax Expense Benefit DeferredFederalStateAndLocalTaxExpenseBenefit	-123261000	USD
CY2020	us-gaap	Deferred Federal State And Local Tax Expense Benefit DeferredFederalStateAndLocalTaxExpenseBenefit	-89170000	USD
CY2019	us-gaap	Deferred Federal State And Local Tax Expense Benefit DeferredFederalStateAndLocalTaxExpenseBenefit	11849000	USD
CY2021	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-43690000	USD
CY2020	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	3346000	USD
CY2019	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-400000	USD
CY2021	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-166951000	USD
CY2020	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-85824000	USD
CY2019	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	11449000	USD
CY2021	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	128582000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	111838000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	155810000	USD
CY2020	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	5027000	USD
CY2021	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	2368042000	USD
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	1577549000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	1849110000	USD
CY2021	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	158269000	USD
CY2020	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	111947000	USD
CY2019	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	149799000	USD
CY2021	us-gaap	Income Tax Reconciliation Tax Exempt Income IncomeTaxReconciliationTaxExemptIncome	23572000	USD
CY2020	us-gaap	Income Tax Reconciliation Tax Exempt Income IncomeTaxReconciliationTaxExemptIncome	1824000	USD
CY2019	us-gaap	Income Tax Reconciliation Tax Exempt Income IncomeTaxReconciliationTaxExemptIncome	3091000	USD
CY2021	us-gaap	Income Tax Reconciliation Nondeductible Expense Meals And Entertainment IncomeTaxReconciliationNondeductibleExpenseMealsAndEntertainment	379000	USD
CY2020	us-gaap	Income Tax Reconciliation Nondeductible Expense Meals And Entertainment IncomeTaxReconciliationNondeductibleExpenseMealsAndEntertainment	547000	USD
CY2019	us-gaap	Income Tax Reconciliation Nondeductible Expense Meals And Entertainment IncomeTaxReconciliationNondeductibleExpenseMealsAndEntertainment	1134000	USD
CY2019	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	3314000	USD
CY2021	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	1998000	USD
CY2020	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	2094000	USD
CY2019	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	1231000	USD
CY2021	us-gaap	Income Tax Reconciliation Prior Year Income Taxes IncomeTaxReconciliationPriorYearIncomeTaxes	-1432000	USD
CY2020	us-gaap	Income Tax Reconciliation Prior Year Income Taxes IncomeTaxReconciliationPriorYearIncomeTaxes	3983000	USD
CY2019	us-gaap	Income Tax Reconciliation Prior Year Income Taxes IncomeTaxReconciliationPriorYearIncomeTaxes	632000	USD
CY2021	us-gaap	Income Tax Reconciliation Nondeductible Expense Other IncomeTaxReconciliationNondeductibleExpenseOther	1190000	USD
CY2020	us-gaap	Income Tax Reconciliation Nondeductible Expense Other IncomeTaxReconciliationNondeductibleExpenseOther	-1736000	USD
CY2019	us-gaap	Income Tax Reconciliation Nondeductible Expense Other IncomeTaxReconciliationNondeductibleExpenseOther	436000	USD
CY2021	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	447000	USD
CY2020	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	0	USD
CY2019	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	0	USD
CY2021	acgl	Income Tax Reconciliation Dividend Withholding Taxes IncomeTaxReconciliationDividendWithholdingTaxes	12211000	USD
CY2020	acgl	Income Tax Reconciliation Dividend Withholding Taxes IncomeTaxReconciliationDividendWithholdingTaxes	7105000	USD
CY2019	acgl	Income Tax Reconciliation Dividend Withholding Taxes IncomeTaxReconciliationDividendWithholdingTaxes	6510000	USD
CY2021	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-40425000	USD
CY2020	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	13190000	USD
CY2019	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	1628000	USD
CY2021	acgl	Reconciliation Of Effective Tax Rate Contingent Consideration ReconciliationOfEffectiveTaxRateContingentConsideration	0	USD
CY2020	acgl	Reconciliation Of Effective Tax Rate Contingent Consideration ReconciliationOfEffectiveTaxRateContingentConsideration	9000	USD
CY2019	acgl	Reconciliation Of Effective Tax Rate Contingent Consideration ReconciliationOfEffectiveTaxRateContingentConsideration	190000	USD
CY2021	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	-5339000	USD
CY2020	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	-2533000	USD
CY2019	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	-6592000	USD
CY2021	acgl	Effective Income Tax Reconciliation Intercompany Loan Writeoff Amount EffectiveIncomeTaxReconciliationIntercompanyLoanWriteoffAmount	0	USD
CY2020	acgl	Effective Income Tax Reconciliation Intercompany Loan Writeoff Amount EffectiveIncomeTaxReconciliationIntercompanyLoanWriteoffAmount	-22083000	USD
CY2019	acgl	Effective Income Tax Reconciliation Intercompany Loan Writeoff Amount EffectiveIncomeTaxReconciliationIntercompanyLoanWriteoffAmount	0	USD
CY2021	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	3878000	USD
CY2020	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-3888000	USD
CY2019	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	619000	USD
CY2021	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	128582000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	111838000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	155810000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	87960000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	67142000	USD
CY2021Q4	acgl	Lloyds Syndicate Uncrystallized Losses Deferred Tax Asset LloydsSyndicateUncrystallizedLossesDeferredTaxAsset	0	USD
CY2020Q4	acgl	Lloyds Syndicate Uncrystallized Losses Deferred Tax Asset LloydsSyndicateUncrystallizedLossesDeferredTaxAsset	2926000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Loss Reserves DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsLossReserves	72001000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Loss Reserves DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsLossReserves	74247000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Unearned Premiums Reserve DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsUnearnedPremiumsReserve	75483000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Unearned Premiums Reserve DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsUnearnedPremiumsReserve	66368000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits	28062000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits	27351000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards Foreign DeferredTaxAssetsTaxCreditCarryforwardsForeign	20058000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards Foreign DeferredTaxAssetsTaxCreditCarryforwardsForeign	19160000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Other DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsOther	755000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Other DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsOther	622000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Goodwill And Intangible Assets DeferredTaxAssetsGoodwillAndIntangibleAssets	0	USD
CY2020Q4	us-gaap	Deferred Tax Assets Goodwill And Intangible Assets DeferredTaxAssetsGoodwillAndIntangibleAssets	14450000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Reserves DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsReserves	10252000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Reserves DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsReserves	10842000	USD
CY2021Q4	acgl	Deferred Tax Assets Depreciation And Amortization DeferredTaxAssetsDepreciationAndAmortization	115041000	USD
CY2020Q4	acgl	Deferred Tax Assets Depreciation And Amortization DeferredTaxAssetsDepreciationAndAmortization	0	USD
CY2021Q4	acgl	Deferred Tax Asset Lease Liability DeferredTaxAssetLeaseLiability	21453000	USD
CY2020Q4	acgl	Deferred Tax Asset Lease Liability DeferredTaxAssetLeaseLiability	23604000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Unrealized Currency Losses DeferredTaxAssetsUnrealizedCurrencyLosses	166000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Unrealized Currency Losses DeferredTaxAssetsUnrealizedCurrencyLosses	165000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Other DeferredTaxAssetsTaxDeferredExpenseOther	0	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Other DeferredTaxAssetsTaxDeferredExpenseOther	2318000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	431231000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	309195000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	43953000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	88255000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	387278000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	220940000	USD
CY2021Q4	us-gaap	Deferred Tax Liabilities Other Finite Lived Assets DeferredTaxLiabilitiesOtherFiniteLivedAssets	0	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Other Finite Lived Assets DeferredTaxLiabilitiesOtherFiniteLivedAssets	495000	USD
CY2021Q4	us-gaap	Deferred Tax Liabilities Tax Deferred Income DeferredTaxLiabilitiesTaxDeferredIncome	1578000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Tax Deferred Income DeferredTaxLiabilitiesTaxDeferredIncome	1751000	USD
CY2021Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssets	70549000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssets	0	USD
CY2021Q4	acgl	Deferred Tax Liability Lloyds Year Of Account Deferral DeferredTaxLiabilityLloydsYearOfAccountDeferral	12514000	USD
CY2020Q4	acgl	Deferred Tax Liability Lloyds Year Of Account Deferral DeferredTaxLiabilityLloydsYearOfAccountDeferral	0	USD
CY2021Q4	acgl	Deferred Tax Liability Contingency Reserve DeferredTaxLiabilityContingencyReserve	49486000	USD
CY2020Q4	acgl	Deferred Tax Liability Contingency Reserve DeferredTaxLiabilityContingencyReserve	64593000	USD
CY2021Q4	us-gaap	Deferred Tax Liabilities Deferred Expense Other Capitalized Costs DeferredTaxLiabilitiesDeferredExpenseOtherCapitalizedCosts	25612000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Deferred Expense Other Capitalized Costs DeferredTaxLiabilitiesDeferredExpenseOtherCapitalizedCosts	42045000	USD
CY2021Q4	acgl	Deferred Tax Liabilities Investment Related DeferredTaxLiabilitiesInvestmentRelated	7492000	USD
CY2020Q4	acgl	Deferred Tax Liabilities Investment Related DeferredTaxLiabilitiesInvestmentRelated	9571000	USD
CY2021Q4	us-gaap	Deferred Tax Liabilities Investments DeferredTaxLiabilitiesInvestments	8377000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Investments DeferredTaxLiabilitiesInvestments	66681000	USD
CY2021Q4	acgl	Deferred Tax L Iabilities Right Of Use Asset DeferredTaxLIabilitiesRightOfUseAsset	17406000	USD
CY2020Q4	acgl	Deferred Tax L Iabilities Right Of Use Asset DeferredTaxLIabilitiesRightOfUseAsset	19239000	USD
CY2021Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	218000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	843000	USD
CY2021Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	193232000	USD
CY2020Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	205218000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	194046000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	15722000	USD
CY2021Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	44000000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	88300000	USD
CY2021	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	0	USD
CY2021Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	2000000	USD
CY2020Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	2008000	USD
CY2019Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	2008000	USD
CY2021	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	0	USD
CY2020	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	0	USD
CY2020	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	0	USD
CY2021	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	0	USD
CY2020	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	0	USD
CY2021	acgl	Unrecognized Tax Benefits Change Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsChangeResultingFromSettlementsWithTaxingAuthorities	0	USD
CY2020	acgl	Unrecognized Tax Benefits Change Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsChangeResultingFromSettlementsWithTaxingAuthorities	0	USD
CY2021Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	2008000	USD
CY2020Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	2008000	USD
CY2021Q4	us-gaap	Accrued Income Taxes Current AccruedIncomeTaxesCurrent	14800000	USD
CY2021	us-gaap	Operating Lease Expense OperatingLeaseExpense	31691000	USD
CY2020	us-gaap	Operating Lease Expense OperatingLeaseExpense	31826000	USD
CY2021	us-gaap	Operating Lease Payments OperatingLeasePayments	32094000	USD
CY2020	us-gaap	Operating Lease Payments OperatingLeasePayments	30365000	USD
CY2021	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	22686000	USD
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	12060000	USD
CY2021Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.039
CY2020Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.039
CY2021Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P5Y10M24D
CY2020Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P5Y9M18D
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	31682000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	25288000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	22102000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	16253000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	13430000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	34173000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	142928000	USD
CY2021Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	16217000	USD
CY2021Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	126711000	USD
CY2021	us-gaap	Operating Lease Expense OperatingLeaseExpense	31700000	USD
CY2020	us-gaap	Operating Lease Expense OperatingLeaseExpense	31800000	USD
CY2019	us-gaap	Operating Lease Expense OperatingLeaseExpense	30500000	USD
CY2021Q4	acgl	Investment Commitments InvestmentCommitments	3000000000	USD
CY2020Q4	acgl	Investment Commitments InvestmentCommitments	2100000000	USD
CY2021Q4	us-gaap	Purchase Commitment Remaining Minimum Amount Committed PurchaseCommitmentRemainingMinimumAmountCommitted	114100000	USD
CY2020Q4	us-gaap	Purchase Commitment Remaining Minimum Amount Committed PurchaseCommitmentRemainingMinimumAmountCommitted	73000000	USD
CY2021Q4	us-gaap	Security Owned And Pledged As Collateral Fair Value SecurityOwnedAndPledgedAsCollateralFairValue	348400000	USD
CY2021Q4	us-gaap	Line Of Credit LineOfCredit	0	USD
CY2020Q4	us-gaap	Line Of Credit LineOfCredit	155687000	USD
CY2020Q4	us-gaap	Advances From Federal Home Loan Banks AdvancesFromFederalHomeLoanBanks	80000000	USD
CY2021Q4	us-gaap	Advances From Federal Home Loan Banks AdvancesFromFederalHomeLoanBanks	80000000	USD
CY2020Q4	us-gaap	Federal Home Loan Bank Advances General Debt Obligations Disclosures Collateral Pledged1 FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1	80200000	USD
CY2021Q4	us-gaap	Federal Home Loan Bank Advances General Debt Obligations Disclosures Collateral Pledged1 FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1	80200000	USD
CY2019Q4	us-gaap	Goodwill Goodwill	326551000	USD
CY2019Q4	us-gaap	Indefinite Lived Intangible Assets Excluding Goodwill IndefiniteLivedIntangibleAssetsExcludingGoodwill	85911000	USD
CY2019Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	325621000	USD
CY2019Q4	us-gaap	Intangible Assets Net Including Goodwill IntangibleAssetsNetIncludingGoodwill	738083000	USD
CY2020	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	0	USD
CY2020	us-gaap	Indefinitelived Intangible Assets Acquired IndefinitelivedIntangibleAssetsAcquired	0	USD
CY2020	us-gaap	Finitelived Intangible Assets Acquired1 FinitelivedIntangibleAssetsAcquired1	39178000	USD
CY2020	acgl	Intangible Assets Including Goodwill Acquired Duringthe Period IntangibleAssetsIncludingGoodwillAcquiredDuringthePeriod	39178000	USD
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	69031000	USD
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	69031000	USD
CY2020	us-gaap	Goodwill Foreign Currency Translation Gain Loss GoodwillForeignCurrencyTranslationGainLoss	11922000	USD
CY2020	us-gaap	Indefinite Lived Intangible Assets Foreign Currency Translation Gain Loss IndefiniteLivedIntangibleAssetsForeignCurrencyTranslationGainLoss	6692000	USD
CY2020	us-gaap	Finite Lived Intangible Assets Foreign Currency Translation Gain Loss FiniteLivedIntangibleAssetsForeignCurrencyTranslationGainLoss	-3247000	USD
CY2020	acgl	Intangible Assets Including Goodwill Foreign Currency Translation And Other Adjustments IntangibleAssetsIncludingGoodwillForeignCurrencyTranslationAndOtherAdjustments	15367000	USD
CY2020Q4	us-gaap	Goodwill Goodwill	314629000	USD
CY2020Q4	us-gaap	Indefinite Lived Intangible Assets Excluding Goodwill IndefiniteLivedIntangibleAssetsExcludingGoodwill	79219000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	299015000	USD
CY2020Q4	us-gaap	Intangible Assets Net Including Goodwill IntangibleAssetsNetIncludingGoodwill	692863000	USD
CY2021	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	31677000	USD
CY2021	us-gaap	Indefinitelived Intangible Assets Acquired IndefinitelivedIntangibleAssetsAcquired	0	USD
CY2021	us-gaap	Finitelived Intangible Assets Acquired1 FinitelivedIntangibleAssetsAcquired1	318459000	USD
CY2021	acgl	Intangible Assets Including Goodwill Acquired Duringthe Period IntangibleAssetsIncludingGoodwillAcquiredDuringthePeriod	350136000	USD
CY2021	us-gaap	Goodwill Foreign Currency Translation Gain Loss GoodwillForeignCurrencyTranslationGainLoss	1441000	USD
CY2021	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	82955000	USD
CY2021	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	82955000	USD
CY2021	acgl	Indefinite Lived Intangible Assets Decrease Due To Deconsolidation IndefiniteLivedIntangibleAssetsDecreaseDueToDeconsolidation	7650000	USD
CY2021	acgl	Indefinite Lived And Finite Lived Intangible Assets Decrease Due To Deconsolidation IndefiniteLivedAndFiniteLivedIntangibleAssetsDecreaseDueToDeconsolidation	7650000	USD
CY2021	us-gaap	Indefinite Lived Intangible Assets Foreign Currency Translation Gain Loss IndefiniteLivedIntangibleAssetsForeignCurrencyTranslationGainLoss	212000	USD
CY2021	us-gaap	Finite Lived Intangible Assets Foreign Currency Translation Gain Loss FiniteLivedIntangibleAssetsForeignCurrencyTranslationGainLoss	5758000	USD
CY2021	acgl	Intangible Assets Including Goodwill Foreign Currency Translation And Other Adjustments IntangibleAssetsIncludingGoodwillForeignCurrencyTranslationAndOtherAdjustments	7411000	USD
CY2021Q4	us-gaap	Goodwill Goodwill	344865000	USD
CY2021Q4	us-gaap	Indefinite Lived Intangible Assets Excluding Goodwill IndefiniteLivedIntangibleAssetsExcludingGoodwill	71357000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	528761000	USD
CY2021Q4	us-gaap	Intangible Assets Net Including Goodwill IntangibleAssetsNetIncludingGoodwill	944983000	USD
CY2021Q4	acgl	Intangible Assets Gross Including Goodwill IntangibleAssetsGrossIncludingGoodwill	1515386000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	571839000	USD
CY2021Q4	acgl	Intangible Assets Including Goodwill Accumulated Foreign Currency And Other Adjustments IntangibleAssetsIncludingGoodwillAccumulatedForeignCurrencyAndOtherAdjustments	1436000	USD
CY2021Q4	us-gaap	Intangible Assets Net Including Goodwill IntangibleAssetsNetIncludingGoodwill	944983000	USD
CY2021Q4	acgl	Intangible Assets Liabilitiesand Goodwill Gross IntangibleAssetsLiabilitiesandGoodwillGross	1515386000	USD
CY2021Q4	acgl	Intangible Assets Liabilitiesand Goodwill Net IntangibleAssetsLiabilitiesandGoodwillNet	944983000	USD
CY2020Q4	acgl	Intangible Assets Liabilitiesand Goodwill Gross IntangibleAssetsLiabilitiesandGoodwillGross	1180860000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	571839000	USD
CY2021Q4	acgl	Intangible Assets Including Goodwill Accumulated Foreign Currency And Other Adjustments IntangibleAssetsIncludingGoodwillAccumulatedForeignCurrencyAndOtherAdjustments	1436000	USD
CY2020Q4	us-gaap	Finite Lived Intangible Assets Accumulated Amortization FiniteLivedIntangibleAssetsAccumulatedAmortization	489828000	USD
CY2020Q4	acgl	Intangible Assets Including Goodwill Accumulated Foreign Currency And Other Adjustments IntangibleAssetsIncludingGoodwillAccumulatedForeignCurrencyAndOtherAdjustments	1831000	USD
CY2020Q4	acgl	Intangible Assets Liabilitiesand Goodwill Net IntangibleAssetsLiabilitiesandGoodwillNet	692863000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	109144000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Two FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo	99620000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	79410000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Four FiniteLivedIntangibleAssetsAmortizationExpenseYearFour	44523000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Five FiniteLivedIntangibleAssetsAmortizationExpenseYearFive	35252000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense After Year Five FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive	160812000	USD
CY2021Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	528761000	USD
CY2021Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	1800000000	shares
CY2021Q4	us-gaap	Common Stock Par Or Stated Value Per Share CommonStockParOrStatedValuePerShare	0.0011
CY2021Q4	us-gaap	Preferred Stock Shares Authorized PreferredStockSharesAuthorized	50000000	shares
CY2021Q4	us-gaap	Preferred Stock Par Or Stated Value Per Share PreferredStockParOrStatedValuePerShare	0.01
CY2020Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	579000841	shares
CY2019Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	574617195	shares
CY2018Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	570737283	shares
CY2021	us-gaap	Stock Issued During Period Shares New Issues StockIssuedDuringPeriodSharesNewIssues	2669229	shares
CY2020	us-gaap	Stock Issued During Period Shares New Issues StockIssuedDuringPeriodSharesNewIssues	2646164	shares
CY2019	us-gaap	Stock Issued During Period Shares New Issues StockIssuedDuringPeriodSharesNewIssues	2835994	shares
CY2021	us-gaap	Stock Issued During Period Shares Restricted Stock Award Net Of Forfeitures StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures	1619780	shares
CY2020	us-gaap	Stock Issued During Period Shares Restricted Stock Award Net Of Forfeitures StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures	1737482	shares
CY2019	us-gaap	Stock Issued During Period Shares Restricted Stock Award Net Of Forfeitures StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures	1043918	shares
CY2021Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	583289850	shares
CY2020Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	579000841	shares
CY2019Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	574617195	shares
CY2021Q4	us-gaap	Treasury Stock Shares TreasuryStockShares	204365956	shares
CY2020Q4	us-gaap	Treasury Stock Shares TreasuryStockShares	172280199	shares
CY2019Q4	us-gaap	Treasury Stock Shares TreasuryStockShares	168997994	shares
CY2021Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	378923894	shares
CY2020Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	406720642	shares
CY2019Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	405619201	shares
CY2021Q4	us-gaap	Treasury Stock Shares TreasuryStockShares	204400000	shares
CY2021Q4	us-gaap	Treasury Stock Value TreasuryStockValue	3800000000	USD
CY2021	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	1234294000	USD
CY2020	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	83472000	USD
CY2019	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	2871000	USD
CY2021	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	31486830	shares
CY2020	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	2850102	shares
CY2019	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	110598	shares
CY2021	us-gaap	Treasury Stock Acquired Average Cost Per Share TreasuryStockAcquiredAverageCostPerShare	39.20
CY2020	us-gaap	Treasury Stock Acquired Average Cost Per Share TreasuryStockAcquiredAverageCostPerShare	29.29
CY2019	us-gaap	Treasury Stock Acquired Average Cost Per Share TreasuryStockAcquiredAverageCostPerShare	25.96
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.242
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.166
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.181
CY2021	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.010
CY2020	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.012
CY2019	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.025
CY2021	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y
CY2020	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y
CY2019	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P6Y
CY2019	us-gaap	Allocated Share Based Compensation Expense Net Of Tax AllocatedShareBasedCompensationExpenseNetOfTax	55502000	USD
CY2021	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	86580000	USD
CY2020	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	69892000	USD
CY2019	us-gaap	Allocated Share Based Compensation Expense AllocatedShareBasedCompensationExpense	63848000	USD
CY2021	us-gaap	Allocated Share Based Compensation Expense Net Of Tax AllocatedShareBasedCompensationExpenseNetOfTax	75667000	USD
CY2020	us-gaap	Allocated Share Based Compensation Expense Net Of Tax AllocatedShareBasedCompensationExpenseNetOfTax	60345000	USD
CY2021	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	60400000	USD
CY2020	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	52000000	USD
CY2019	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	44800000	USD
CY2021Q4	us-gaap	Supplementary Insurance Information Deferred Policy Acquisition Costs SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts	901841000	USD
CY2021Q4	us-gaap	Supplementary Insurance Information Liability For Future Policy Benefits Losses Claims And Loss Expense Reserves SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves	17757156000	USD
CY2021Q4	us-gaap	Supplementary Insurance Information Unearned Premiums SupplementaryInsuranceInformationUnearnedPremiums	6011942000	USD
CY2021	us-gaap	Supplementary Insurance Information Premium Revenue SupplementaryInsuranceInformationPremiumRevenue	8082298000	USD
CY2021	us-gaap	Supplementary Insurance Information Benefits Claims Losses And Settlement Expense SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense	4584803000	USD
CY2021	us-gaap	Supplementary Insurance Information Amortization Of Deferred Policy Acquisition Costs SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts	1303178000	USD
CY2021	us-gaap	Supplementary Insurance Information Other Operating Expense SupplementaryInsuranceInformationOtherOperatingExpense	998595000	USD
CY2021	us-gaap	Supplementary Insurance Information Premiums Written SupplementaryInsuranceInformationPremiumsWritten	9018337000	USD
CY2020Q4	us-gaap	Supplementary Insurance Information Deferred Policy Acquisition Costs SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts	790708000	USD
CY2020Q4	us-gaap	Supplementary Insurance Information Liability For Future Policy Benefits Losses Claims And Loss Expense Reserves SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves	16513928000	USD
CY2020Q4	us-gaap	Supplementary Insurance Information Unearned Premiums SupplementaryInsuranceInformationUnearnedPremiums	4838965000	USD
CY2020	us-gaap	Supplementary Insurance Information Premium Revenue SupplementaryInsuranceInformationPremiumRevenue	6991935000	USD
CY2020	us-gaap	Supplementary Insurance Information Benefits Claims Losses And Settlement Expense SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense	4689599000	USD
CY2020	us-gaap	Supplementary Insurance Information Amortization Of Deferred Policy Acquisition Costs SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts	1004842000	USD
CY2020	us-gaap	Supplementary Insurance Information Other Operating Expense SupplementaryInsuranceInformationOtherOperatingExpense	875176000	USD
CY2020	us-gaap	Supplementary Insurance Information Premiums Written SupplementaryInsuranceInformationPremiumsWritten	7437716000	USD
CY2019Q4	us-gaap	Supplementary Insurance Information Deferred Policy Acquisition Costs SupplementaryInsuranceInformationDeferredPolicyAcquisitionCosts	633400000	USD
CY2019Q4	us-gaap	Supplementary Insurance Information Liability For Future Policy Benefits Losses Claims And Loss Expense Reserves SupplementaryInsuranceInformationLiabilityForFuturePolicyBenefitsLossesClaimsAndLossExpenseReserves	13891842000	USD
CY2019Q4	us-gaap	Supplementary Insurance Information Unearned Premiums SupplementaryInsuranceInformationUnearnedPremiums	4339549000	USD
CY2019	us-gaap	Supplementary Insurance Information Premium Revenue SupplementaryInsuranceInformationPremiumRevenue	5786498000	USD
CY2019	us-gaap	Supplementary Insurance Information Benefits Claims Losses And Settlement Expense SupplementaryInsuranceInformationBenefitsClaimsLossesAndSettlementExpense	3133452000	USD
CY2019	us-gaap	Supplementary Insurance Information Amortization Of Deferred Policy Acquisition Costs SupplementaryInsuranceInformationAmortizationOfDeferredPolicyAcquisitionCosts	840945000	USD
CY2019	us-gaap	Supplementary Insurance Information Other Operating Expense SupplementaryInsuranceInformationOtherOperatingExpense	800997000	USD
CY2019	us-gaap	Supplementary Insurance Information Premiums Written SupplementaryInsuranceInformationPremiumsWritten	6039067000	USD
CY2021	us-gaap	Direct Premiums Written DirectPremiumsWritten	7706832000	USD
CY2021	us-gaap	Ceded Premiums Written CededPremiumsWritten	3734150000	USD
CY2021	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	5045655000	USD
CY2021	us-gaap	Premiums Written Net PremiumsWrittenNet	9018337000	USD
CY2021	acgl	Premiums Written Percentage Assumed To Net PremiumsWrittenPercentageAssumedToNet	0.559
CY2020	us-gaap	Direct Premiums Written DirectPremiumsWritten	6553910000	USD
CY2020	us-gaap	Ceded Premiums Written CededPremiumsWritten	2650352000	USD
CY2020	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	3534158000	USD
CY2020	us-gaap	Premiums Written Net PremiumsWrittenNet	7437716000	USD
CY2020	acgl	Premiums Written Percentage Assumed To Net PremiumsWrittenPercentageAssumedToNet	0.475
CY2019	us-gaap	Direct Premiums Written DirectPremiumsWritten	5681523000	USD
CY2019	us-gaap	Ceded Premiums Written CededPremiumsWritten	2099893000	USD
CY2019	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	2457437000	USD
CY2019	us-gaap	Premiums Written Net PremiumsWrittenNet	6039067000	USD
CY2019	acgl	Premiums Written Percentage Assumed To Net PremiumsWrittenPercentageAssumedToNet	0.407

Files In Submission

Name	View Source	Status
0000947484-22-000015-index-headers.html	Edgar Link	pending
0000947484-22-000015-index.html	Edgar Link	pending
0000947484-22-000015.txt	Edgar Link	pending
0000947484-22-000015-xbrl.zip	Edgar Link	pending
a2021ex21.htm	Edgar Link	pending
a2021ex23.htm	Edgar Link	pending
a2021ex24.htm	Edgar Link	pending
a2021ex311.htm	Edgar Link	pending
a2021ex312.htm	Edgar Link	pending
a2021ex321.htm	Edgar Link	pending
a2021ex322.htm	Edgar Link	pending
acgl-20211231.htm	Edgar Link	pending
acgl-20211231.xsd	Edgar Link	pending
acgl-20211231_cal.xml	Edgar Link	unprocessable
acgl-20211231_def.xml	Edgar Link	unprocessable
acgl-20211231_g1.jpg	Edgar Link	pending
acgl-20211231_g2.jpg	Edgar Link	pending
acgl-20211231_htm.xml	Edgar Link	completed
acgl-20211231_lab.xml	Edgar Link	unprocessable
acgl-20211231_pre.xml	Edgar Link	unprocessable
ex1023.htm	Edgar Link	pending
ex48-descriptionofsecuriti.htm	Edgar Link	pending
FilingSummary.xml	Edgar Link	unprocessable
Financial_Report.xlsx	Edgar Link	pending
MetaLinks.json	Edgar Link	pending
R1.htm	Edgar Link	pending
R10.htm	Edgar Link	pending
R100.htm	Edgar Link	pending
R101.htm	Edgar Link	pending
R102.htm	Edgar Link	pending
R103.htm	Edgar Link	pending
R104.htm	Edgar Link	pending
R105.htm	Edgar Link	pending
R106.htm	Edgar Link	pending
R107.htm	Edgar Link	pending
R108.htm	Edgar Link	pending
R109.htm	Edgar Link	pending
R11.htm	Edgar Link	pending
R110.htm	Edgar Link	pending
R111.htm	Edgar Link	pending
R112.htm	Edgar Link	pending
R113.htm	Edgar Link	pending
R114.htm	Edgar Link	pending
R115.htm	Edgar Link	pending
R116.htm	Edgar Link	pending
R117.htm	Edgar Link	pending
R118.htm	Edgar Link	pending
R119.htm	Edgar Link	pending
R12.htm	Edgar Link	pending
R120.htm	Edgar Link	pending
R121.htm	Edgar Link	pending
R122.htm	Edgar Link	pending
R123.htm	Edgar Link	pending
R124.htm	Edgar Link	pending
R125.htm	Edgar Link	pending
R126.htm	Edgar Link	pending
R127.htm	Edgar Link	pending
R128.htm	Edgar Link	pending
R129.htm	Edgar Link	pending
R13.htm	Edgar Link	pending
R130.htm	Edgar Link	pending
R131.htm	Edgar Link	pending
R132.htm	Edgar Link	pending
R133.htm	Edgar Link	pending
R134.htm	Edgar Link	pending
R135.htm	Edgar Link	pending
R136.htm	Edgar Link	pending
R137.htm	Edgar Link	pending
R138.htm	Edgar Link	pending
R139.htm	Edgar Link	pending
R14.htm	Edgar Link	pending
R140.htm	Edgar Link	pending
R141.htm	Edgar Link	pending
R142.htm	Edgar Link	pending
R143.htm	Edgar Link	pending
R144.htm	Edgar Link	pending
R145.htm	Edgar Link	pending
R146.htm	Edgar Link	pending
R147.htm	Edgar Link	pending
R148.htm	Edgar Link	pending
R149.htm	Edgar Link	pending
R15.htm	Edgar Link	pending
R150.htm	Edgar Link	pending
R16.htm	Edgar Link	pending
R17.htm	Edgar Link	pending
R18.htm	Edgar Link	pending
R19.htm	Edgar Link	pending
R2.htm	Edgar Link	pending
R20.htm	Edgar Link	pending
R21.htm	Edgar Link	pending
R22.htm	Edgar Link	pending
R23.htm	Edgar Link	pending
R24.htm	Edgar Link	pending
R25.htm	Edgar Link	pending
R26.htm	Edgar Link	pending
R27.htm	Edgar Link	pending
R28.htm	Edgar Link	pending
R29.htm	Edgar Link	pending
R3.htm	Edgar Link	pending
R30.htm	Edgar Link	pending
R31.htm	Edgar Link	pending
R32.htm	Edgar Link	pending
R33.htm	Edgar Link	pending
R34.htm	Edgar Link	pending
R35.htm	Edgar Link	pending
R36.htm	Edgar Link	pending
R37.htm	Edgar Link	pending
R38.htm	Edgar Link	pending
R39.htm	Edgar Link	pending
R4.htm	Edgar Link	pending
R40.htm	Edgar Link	pending
R41.htm	Edgar Link	pending
R42.htm	Edgar Link	pending
R43.htm	Edgar Link	pending
R44.htm	Edgar Link	pending
R45.htm	Edgar Link	pending
R46.htm	Edgar Link	pending
R47.htm	Edgar Link	pending
R48.htm	Edgar Link	pending
R49.htm	Edgar Link	pending
R5.htm	Edgar Link	pending
R50.htm	Edgar Link	pending
R51.htm	Edgar Link	pending
R52.htm	Edgar Link	pending
R53.htm	Edgar Link	pending
R54.htm	Edgar Link	pending
R55.htm	Edgar Link	pending
R56.htm	Edgar Link	pending
R57.htm	Edgar Link	pending
R58.htm	Edgar Link	pending
R59.htm	Edgar Link	pending
R6.htm	Edgar Link	pending
R60.htm	Edgar Link	pending
R61.htm	Edgar Link	pending
R62.htm	Edgar Link	pending
R63.htm	Edgar Link	pending
R64.htm	Edgar Link	pending
R65.htm	Edgar Link	pending
R66.htm	Edgar Link	pending
R67.htm	Edgar Link	pending
R68.htm	Edgar Link	pending
R69.htm	Edgar Link	pending
R7.htm	Edgar Link	pending
R70.htm	Edgar Link	pending
R71.htm	Edgar Link	pending
R72.htm	Edgar Link	pending
R73.htm	Edgar Link	pending
R74.htm	Edgar Link	pending
R75.htm	Edgar Link	pending
R76.htm	Edgar Link	pending
R77.htm	Edgar Link	pending
R78.htm	Edgar Link	pending
R79.htm	Edgar Link	pending
R8.htm	Edgar Link	pending
R80.htm	Edgar Link	pending
R81.htm	Edgar Link	pending
R82.htm	Edgar Link	pending
R83.htm	Edgar Link	pending
R84.htm	Edgar Link	pending
R85.htm	Edgar Link	pending
R86.htm	Edgar Link	pending
R87.htm	Edgar Link	pending
R88.htm	Edgar Link	pending
R89.htm	Edgar Link	pending
R9.htm	Edgar Link	pending
R90.htm	Edgar Link	pending
R91.htm	Edgar Link	pending
R92.htm	Edgar Link	pending
R93.htm	Edgar Link	pending
R94.htm	Edgar Link	pending
R95.htm	Edgar Link	pending
R96.htm	Edgar Link	pending
R97.htm	Edgar Link	pending
R98.htm	Edgar Link	pending
R99.htm	Edgar Link	pending
report.css	Edgar Link	pending
Show.js	Edgar Link	pending

Create your account

Find Stocks Worth Researching

Deeply Understand Businesses

Value Businesses Intelligently

$ACGL
ARCH CAPITAL GROUP LTD. Stock $acgl

2021 Q4 Form 10-K Financial Statement

#000094748422000015 Filed on February 25, 2022

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$ACGL ARCH CAPITAL GROUP LTD. Stock $acgl

2021 Q4 Form 10-K Financial Statement

#000094748422000015 Filed on February 25, 2022

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$ACGL
ARCH CAPITAL GROUP LTD. Stock $acgl