$AJG
Arthur J. Gallagher & Co. Stock $ajg

$ajg Overview Financials Valuation SEC Filings Company Website

2018 Q4 Form 10-K Financial Statement

#000119312519032304 Filed on February 08, 2019

Income Statement

Concept	2018 Q4	2018 Q3	2018 Q2
Revenue	$1.657B	$1.779B	$1.660B
YoY Change	9.08%	11.6%	11.47%
Cost Of Revenue	$1.228B	$1.312B	$1.202B
YoY Change	7.51%	12.53%	9.34%
Gross Profit	$429.0M	$466.7M	$458.5M
YoY Change	13.85%	9.04%	17.47%
Gross Profit Margin	25.88%	26.24%	27.61%
Selling, General & Admin
YoY Change
% of Gross Profit
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$109.8M	$33.40M	$30.80M
YoY Change	13.66%	9.51%	1.99%
% of Gross Profit	25.59%	7.16%	6.72%
Operating Expenses	$349.3M	$227.7M	$222.8M
YoY Change	10.4%	8.95%	9.11%
Operating Profit	$79.70M	$239.0M	$235.7M
YoY Change	31.95%	9.13%	26.65%
Interest Expense	-$36.50M	$36.70M	$33.90M
YoY Change	16.99%	16.88%	7.28%
% of Operating Profit	-45.8%	15.36%	14.38%
Other Income/Expense, Net
YoY Change
Pretax Income	$43.20M	$90.30M	$103.6M
YoY Change	47.95%	17.43%	91.5%
Income Tax	-$81.40M	-$48.10M	-$20.10M
% Of Pretax Income	-188.43%	-53.27%	-19.4%
Net Earnings	$117.3M	$127.6M	$114.9M
YoY Change	64.06%	14.95%	64.14%
Net Earnings / Revenue	7.08%	7.17%	6.92%
Basic Earnings Per Share		$0.70	$0.63
Diluted Earnings Per Share	$624.9K	$0.68	$0.62
COMMON SHARES
Basic Shares Outstanding		183.3M shares	182.4M shares
Diluted Shares Outstanding

Balance Sheet

Concept	2018 Q4	2018 Q3	2018 Q2
SHORT-TERM ASSETS
Cash & Short-Term Investments	$607.0M	$605.0M	$652.0M
YoY Change	-10.87%	7.08%	10.88%
Cash & Equivalents	$607.2M	$605.0M	$652.2M
Short-Term Investments
Other Short-Term Assets	$1.024B	$951.5M	$878.1M
YoY Change	16.2%	40.01%	32.22%
Inventory
Prepaid Expenses	$108.2M	$99.90M	$95.40M
Receivables
Other Receivables
Total Short-Term Assets	$8.119B	$8.084B	$8.365B
YoY Change	11.68%	58.9%	63.79%
LONG-TERM ASSETS
Property, Plant & Equipment	$436.9M	$429.3M	$427.6M
YoY Change	5.99%	3.85%	10.32%
Goodwill	$4.626B	$4.501B	$4.404B
YoY Change	11.06%	8.19%	10.4%
Intangibles	$1.773B	$1.772B	$1.731B
YoY Change	7.81%	6.04%	4.11%
Long-Term Investments
YoY Change
Other Assets	$573.6M	$584.6M	$586.7M
YoY Change	1.15%	4.47%	4.53%
Total Long-Term Assets	$8.215B	$8.031B	$7.866B
YoY Change	7.53%	3.98%	5.4%
TOTAL ASSETS
Total Short-Term Assets	$8.119B	$8.084B	$8.365B
Total Long-Term Assets	$8.215B	$8.031B	$7.866B
Total Assets	$16.33B	$16.11B	$16.23B
YoY Change	9.55%	25.79%	29.13%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$5.740B	$5.694B	$5.983B
YoY Change	15.12%	62.27%	68.73%
Accrued Expenses	$1.037B	$938.0M	$841.0M
YoY Change	9.39%	22.14%	18.28%
Deferred Revenue
YoY Change
Short-Term Debt	$365.0M	$230.0M	$235.0M
YoY Change	25.86%	84.0%	-36.14%
Long-Term Debt Due	$365.0M	$230.0M	$235.0M
YoY Change	25.86%	84.0%	-36.14%
Total Short-Term Liabilities	$7.694B	$7.423B	$7.569B
YoY Change	14.31%	57.75%	55.8%
LONG-TERM LIABILITIES
Long-Term Debt	$3.091B	$3.141B	$3.141B
YoY Change	14.84%	14.57%	18.76%
Other Long-Term Liabilities	$900.9M	$862.1M	$931.2M
YoY Change	-19.03%	-27.63%	-19.5%
Total Long-Term Liabilities	$3.992B	$4.003B	$4.072B
YoY Change	4.94%	1.79%	7.12%
TOTAL LIABILITIES
Total Short-Term Liabilities	$7.694B	$7.423B	$7.569B
Total Long-Term Liabilities	$3.992B	$4.003B	$4.072B
Total Liabilities	$11.76B	$11.50B	$11.72B
YoY Change	10.88%	33.15%	35.31%
SHAREHOLDERS EQUITY
Retained Earnings	$1.559B	$1.518B	$1.466B
YoY Change	27.57%	42.89%	46.18%
Common Stock	$3.726B	$3.700B	$3.629B
YoY Change	4.39%	4.33%	3.58%
Preferred Stock
YoY Change
Treasury Stock (at cost)
YoY Change
Treasury Stock Shares
Shareholders Equity	$4.499B	$4.545B	$4.444B
YoY Change
Total Liabilities & Shareholders Equity	$16.33B	$16.11B	$16.23B
YoY Change	9.55%	25.79%	29.13%

Cashflow Statement

Concept	2018 Q4	2018 Q3	2018 Q2
OPERATING ACTIVITIES
Net Income	$117.3M	$127.6M	$114.9M
YoY Change	64.06%	14.95%	64.14%
Depreciation, Depletion And Amortization	$109.8M	$33.40M	$30.80M
YoY Change	13.66%	9.51%	1.99%
Cash From Operating Activities	$260.5M	$191.3M	$530.9M
YoY Change	-0.19%	-42.43%	116.34%
INVESTING ACTIVITIES
Capital Expenditures	-$33.60M	-$28.10M	-$31.60M
YoY Change	-5.08%	-0.35%	-12.95%
Acquisitions
YoY Change
Other Investing Activities	-$222.9M	-$180.0M	-$327.2M
YoY Change	203.68%	98.68%	325.49%
Cash From Investing Activities	-$256.5M	-$208.1M	-$358.8M
YoY Change	135.75%	75.17%	216.96%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	5.200M	-44.80M	132.1M
YoY Change	-533.33%	-72.95%	33.3%
NET CHANGE
Cash From Operating Activities	260.5M	191.3M	530.9M
Cash From Investing Activities	-256.5M	-208.1M	-358.8M
Cash From Financing Activities	5.200M	-44.80M	132.1M
Net Change In Cash	9.200M	-61.60M	304.2M
YoY Change	-93.91%	-228.6%	31.52%
FREE CASH FLOW
Cash From Operating Activities	$260.5M	$191.3M	$530.9M
Capital Expenditures	-$33.60M	-$28.10M	-$31.60M
Free Cash Flow	$294.1M	$219.4M	$562.5M
YoY Change	-0.78%	-39.14%	99.68%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
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CY2018Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets	1293400000
CY2018Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Liabilities Other BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther	3100000
CY2018Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets	26200000
CY2018Q4	us-gaap	Capitalized Contract Cost Net CapitalizedContractCostNet	91600000
CY2018Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Net BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet	1014900000
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	2236800000
CY2018Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	400000000	shares
CY2018Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	184000000	shares
CY2018Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	184000000	shares
CY2018Q4	us-gaap	Common Stock Value CommonStockValue	184000000
CY2018Q4	us-gaap	Construction In Progress Gross ConstructionInProgressGross	14900000
CY2018Q4	us-gaap	Contract With Customer Liability ContractWithCustomerLiability	457700000
CY2018Q4	us-gaap	Deferred Rent Credit Current DeferredRentCreditCurrent	4200000
CY2018Q4	us-gaap	Deferred Tax Assets Investments DeferredTaxAssetsInvestments	1500000
CY2018Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	3400000
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Accrued Liabilities DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities	63800000
CY2018Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	67400000
CY2018Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets	297600000
CY2018Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Four DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour	16500000
CY2018Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Two DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo	16100000
CY2018Q4	us-gaap	Deferred Tax Assets Capital Loss Carryforwards DeferredTaxAssetsCapitalLossCarryforwards	12200000
CY2018Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	699300000
CY2018Q4	us-gaap	Deferred Tax Assets Net Noncurrent DeferredTaxAssetsNetNoncurrent	806200000
CY2018Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	36800000
CY2018Q4	us-gaap	Defined Benefit Plan Accumulated Other Comprehensive Income Net Gains Losses Before Tax DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax	-76000000
CY2018Q4	us-gaap	Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate	0.0400	pure
CY2018Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Next Twelve Months DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths	15800000
CY2018Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Five DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive	16600000
CY2018Q4	us-gaap	Deferred Revenue Current DeferredRevenueCurrent	379300000
CY2018Q4	us-gaap	Deferred Tax Assets Goodwill And Intangible Assets DeferredTaxAssetsGoodwillAndIntangibleAssets	48800000
CY2018Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	1212000000
CY2018Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	1144600000
CY2018Q4	us-gaap	Defined Benefit Plan Expected Amortization Next Fiscal Year DefinedBenefitPlanExpectedAmortizationNextFiscalYear	7200000
CY2018Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Five Fiscal Years Thereafter DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter	82800000
CY2018Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Three DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree	16300000
CY2018Q4	us-gaap	Defined Benefit Plan Fair Value Of Plan Assets DefinedBenefitPlanFairValueOfPlanAssets	220000000
CY2018Q4	us-gaap	Derivative Assets Noncurrent DerivativeAssetsNoncurrent	5700000
CY2018Q4	us-gaap	Derivative Liabilities Current DerivativeLiabilitiesCurrent	17900000
CY2018Q4	us-gaap	Derivative Liabilities Noncurrent DerivativeLiabilitiesNoncurrent	7900000
CY2018Q4	us-gaap	Deferred Revenue DeferredRevenue	457700000
CY2018Q4	us-gaap	Deferred Revenue Noncurrent DeferredRevenueNoncurrent	78400000
CY2018Q4	us-gaap	Deferred Tax Assets Hedging Transactions DeferredTaxAssetsHedgingTransactions	1900000
CY2018Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	12200000
CY2018Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	445300000
CY2018Q4	us-gaap	Deferred Tax Liabilities Undistributed Foreign Earnings DeferredTaxLiabilitiesUndistributedForeignEarnings	631000000
CY2018Q4	us-gaap	Defined Benefit Plan Amounts Recognized In Balance Sheet DefinedBenefitPlanAmountsRecognizedInBalanceSheet	42800000
CY2018Q4	us-gaap	Defined Benefit Plan Benefit Obligation DefinedBenefitPlanBenefitObligation	253200000
CY2018Q4	us-gaap	Defined Benefit Plan Funded Status Of Plan DefinedBenefitPlanFundedStatusOfPlan	-33200000
CY2018Q4	us-gaap	Derivative Asset Notional Amount DerivativeAssetNotionalAmount	9600000
CY2018Q4	us-gaap	Defined Benefit Plan Weighted Average Asset Allocations DefinedBenefitPlanWeightedAverageAssetAllocations	1.000	pure
CY2018Q4	us-gaap	Derivative Assets Current DerivativeAssetsCurrent	3900000
CY2018Q4	invest	Derivative Notional Amount DerivativeNotionalAmount	901400000
CY2018Q4	us-gaap	Derivative Liability Notional Amount DerivativeLiabilityNotionalAmount	25800000
CY2018Q4	us-gaap	Escrow Deposit EscrowDeposit	71400000
CY2018Q4	us-gaap	Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized	30800000
CY2018Q4	us-gaap	Equity Method Investment Ownership Percentage EquityMethodInvestmentOwnershipPercentage	0.50	pure
CY2018Q4	us-gaap	Equity Method Investment Summarized Financial Information Assets EquityMethodInvestmentSummarizedFinancialInformationAssets	59500000
CY2018Q4	us-gaap	Finite Lived Trade Names Gross FiniteLivedTradeNamesGross	61500000
CY2018Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	287200000
CY2018Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Four FiniteLivedIntangibleAssetsAmortizationExpenseYearFour	222200000
CY2018Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense After Year Five FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive	547400000
CY2018Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Five FiniteLivedIntangibleAssetsAmortizationExpenseYearFive	198200000
CY2018Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	247300000
CY2018Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Two FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo	270700000
CY2018Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	1773000000
CY2018Q4	us-gaap	Finite Lived Noncompete Agreements Gross FiniteLivedNoncompeteAgreementsGross	5300000
CY2018Q4	us-gaap	Goodwill Goodwill	4625600000
CY2018Q4	us-gaap	Furniture And Fixtures Gross FurnitureAndFixturesGross	116900000
CY2018Q4	us-gaap	Intangible Assets Net Excluding Goodwill IntangibleAssetsNetExcludingGoodwill	1773000000
CY2018Q4	us-gaap	Liabilities Current LiabilitiesCurrent	7693600000
CY2018Q4	us-gaap	Leasehold Improvements Gross LeaseholdImprovementsGross	132100000
CY2018Q4	us-gaap	Liabilities Liabilities	11764300000
CY2018Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	16334000000
CY2018Q4	us-gaap	Long Term Debt LongTermDebt	19900000
CY2018Q4	us-gaap	Minority Interest MinorityInterest	70800000
CY2018Q4	us-gaap	Long Term Debt Noncurrent LongTermDebtNoncurrent	3091400000
CY2018Q4	us-gaap	Machinery And Equipment Gross MachineryAndEquipmentGross	30000000
CY2018Q4	us-gaap	Other Assets Current OtherAssetsCurrent	1024400000
CY2018Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	573600000
CY2018Q4	us-gaap	Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent	33200000
CY2018Q4	us-gaap	Prepaid Expense Current PrepaidExpenseCurrent	108200000
CY2018Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	900900000
CY2018Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	436900000
CY2018Q4	us-gaap	Premiums And Other Receivables Net PremiumsAndOtherReceivablesNet	4857500000
CY2018Q4	us-gaap	Reinsurance Recoverables ReinsuranceRecoverables	68500000
CY2018Q4	us-gaap	Property Plant And Equipment Other PropertyPlantAndEquipmentOther	12400000
CY2018Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	941700000
CY2018Q4	us-gaap	Restricted Cash Current RestrictedCashCurrent	1629600000
CY2018Q4	us-gaap	Revenue Remaining Performance Obligation RevenueRemainingPerformanceObligation	457700000
CY2018Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	1558600000
CY2018Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Intrinsic Value1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1	64400000
CY2018Q4	us-gaap	Short Term Borrowings ShortTermBorrowings	365000000
CY2018Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	4569700000
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber	2100000	shares
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice	42.84
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	8800000	shares
CY2018Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	50.16
CY2018Q4	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Exercisable Options Weighted Average Exercise Price1 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1	42.84
CY2018Q4	us-gaap	Unamortized Debt Issuance Expense UnamortizedDebtIssuanceExpense	6600000
CY2018Q4	us-gaap	Unbilled Contracts Receivable UnbilledContractsReceivable	496200000
CY2018Q4	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Number Of Exercisable Options ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions	2100000	shares
CY2018Q4	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Number Of Outstanding Options ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions	8800000	shares
CY2018Q4	us-gaap	Stockholders Equity StockholdersEquity	4498900000
CY2018Q4	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	2900000
CY2018Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	10700000
CY2018Q4	us-gaap	Unrecognized Tax Benefits That Would Impact Effective Tax Rate UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate	8800000
CY2018Q4	ajg	Accrued Supplemental Direct Bill And Other Receivables Current AccruedSupplementalDirectBillAndOtherReceivablesCurrent	348200000
CY2018Q4	ajg	Semi Annual Payments Of Interest SemiAnnualPaymentsOfInterest	3617000000
CY2018Q4	ajg	Premium Financing Borrowings PremiumFinancingBorrowings	154000000
CY2018Q4	ajg	Premiums Payable To Underwriting Enterprises PremiumsPayableToUnderwritingEnterprises	5740200000
CY2018Q4	ajg	Liabilities Recorded On Self Insurance LiabilitiesRecordedOnSelfInsurance	15800000
CY2018Q4	ajg	Expiration Lists ExpirationLists	381800000
CY2018Q4	ajg	Deferred Tax Assets Alternative Minimum Tax And Other Credit Carryforwards DeferredTaxAssetsAlternativeMinimumTaxAndOtherCreditCarryforwards	856900000
CY2018Q4	ajg	Deferred Tax Liabilities Other Prepaid Items DeferredTaxLiabilitiesOtherPrepaidItems	10600000
CY2018Q4	ajg	Business Acquisition Cost Of Acquired Entity Purchase Price Net BusinessAcquisitionCostOfAcquiredEntityPurchasePriceNet	1014900000
CY2018Q4	ajg	Semi Annual Payments Of Interest Net SemiAnnualPaymentsOfInterestNet	3610400000
CY2018Q4	ajg	Land And Buildings Gross LandAndBuildingsGross	144300000
CY2018Q4	ajg	Business Acquisitions Purchase Price Allocation Goodwill Amount BusinessAcquisitionsPurchasePriceAllocationGoodwillAmount	584600000
CY2018Q4	ajg	Deferred Tax Assets Accrued And Unfunded Compensation And Employee Benefits DeferredTaxAssetsAccruedAndUnfundedCompensationAndEmployeeBenefits	158800000
CY2018Q4	ajg	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Aggregate Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingAggregateIntrinsicValue	206800000
CY2018Q4	ajg	Equity Method Investment Summarized Financial Information Funding Commitments EquityMethodInvestmentSummarizedFinancialInformationFundingCommitments	0
CY2018Q4	ajg	Accrued Compensation And Other Accrued Liabilities AccruedCompensationAndOtherAccruedLiabilities	1055100000
CY2018Q4	ajg	Deferred Tax Liabilities Depreciable Fixed Assets DeferredTaxLiabilitiesDepreciableFixedAssets	25400000
CY2018Q4	ajg	Deferred Tax Liabilities Investment Related Partnerships DeferredTaxLiabilitiesInvestmentRelatedPartnerships	13600000
CY2018Q4	ajg	Maximum Potential Earnout Payable MaximumPotentialEarnoutPayable	201500000
CY2018Q4	ajg	Computer Equipment Gross ComputerEquipmentGross	145100000
CY2018Q4	ajg	Refined Coal Production Related Receivables Current RefinedCoalProductionRelatedReceivablesCurrent	160200000
CY2018Q4	ajg	Deferred Tax Assets Accrued Pension Liability DeferredTaxAssetsAccruedPensionLiability	11500000
CY2018Q4	ajg	Share Based Compensation Arrangement By Share Based Payment Award Options Non Vested And Expected To Vest Number Of Shares ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonVestedAndExpectedToVestNumberOfShares	6500000	shares
CY2018Q4	ajg	Number Of Commercial Clean Coal Production Facilities NumberOfCommercialCleanCoalProductionFacilities	34	pure
CY2018Q4	ajg	Number Of Certified Low Income Housing Developments Investment NumberOfCertifiedLowIncomeHousingDevelopmentsInvestment	8	Investment
CY2018Q4	ajg	Share Based Compensation Arrangement By Share Based Payment Award Options Nonvested And Expected To Vest Exercisable Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsNonvestedAndExpectedToVestExercisableWeightedAverageExercisePrice	52.14
CY2018Q4	ajg	Number Of Square Feet NumberOfSquareFeet	360000	sqft
CY2018Q4	ajg	Deferred Tax Liabilities Revenue Recognition DeferredTaxLiabilitiesRevenueRecognition	-98100000
CY2018Q4	ajg	Sharebased Compensation Arrangement Non Vested And Expected To Vest Outstanding Aggregate Intrinsic Value SharebasedCompensationArrangementNonVestedAndExpectedToVestOutstandingAggregateIntrinsicValue	140300000
CY2016Q1	us-gaap	Cumulative Effect On Retained Earnings Net Of Tax1 CumulativeEffectOnRetainedEarningsNetOfTax1	125300000
CY2017	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	1300000	shares
CY2017	us-gaap	Adjustment For Amortization AdjustmentForAmortization	264700000
CY2017	us-gaap	Amount Recognized In Net Periodic Benefit Cost And Other Comprehensive Income Loss Before Tax AmountRecognizedInNetPeriodicBenefitCostAndOtherComprehensiveIncomeLossBeforeTax	-1500000
CY2017	us-gaap	Business Acquisition Pro Forma Earnings Per Share Basic BusinessAcquisitionProFormaEarningsPerShareBasic	2.74
CY2017	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	6572400000
CY2017	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	10700000
CY2017	us-gaap	Assumed Premiums Earned AssumedPremiumsEarned	4500000
CY2017	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	5000000
CY2017	us-gaap	Business Combination Separately Recognized Transactions Additional Disclosures Acquisition Cost Expensed BusinessCombinationSeparatelyRecognizedTransactionsAdditionalDisclosuresAcquisitionCostExpensed	20200000
CY2017	us-gaap	Business Acquisition Pro Forma Earnings Per Share Diluted BusinessAcquisitionProFormaEarningsPerShareDiluted	2.71
CY2017	us-gaap	Ceded Premiums Earned CededPremiumsEarned	64900000
CY2017	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	36400000
CY2017	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	367400000
CY2017	us-gaap	Ceded Premiums Written CededPremiumsWritten	65700000
CY2017	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.56
CY2017	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	681700000
CY2017	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	718100000
CY2017	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate	0.0400	pure
CY2017	us-gaap	Defined Benefit Plan Interest Cost DefinedBenefitPlanInterestCost	10000000
CY2017	us-gaap	Defined Benefit Plan Actual Return On Plan Assets DefinedBenefitPlanActualReturnOnPlanAssets	24700000
CY2017	us-gaap	Defined Benefit Plan Amortization Of Gains Losses DefinedBenefitPlanAmortizationOfGainsLosses	-5000000
CY2017	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	362800000
CY2017	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	7100000
CY2017	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	25900000
CY2017	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	11600000
CY2017	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-14300000
CY2017	us-gaap	Contract With Customer Liability Increase Decrease For Contract Acquired In Business Combination ContractWithCustomerLiabilityIncreaseDecreaseForContractAcquiredInBusinessCombination	5900000
CY2017	us-gaap	Cost Of Goods And Services Sold CostOfGoodsAndServicesSold	1635900000
CY2017	us-gaap	Costs And Expenses CostsAndExpenses	5889200000
CY2017	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-183500000
CY2017	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-3900000
CY2017	us-gaap	Defined Benefit Plan Contributions By Employer DefinedBenefitPlanContributionsByEmployer	0
CY2017	us-gaap	Defined Benefit Plan Expected Return On Plan Assets DefinedBenefitPlanExpectedReturnOnPlanAssets	14000000
CY2017	us-gaap	Defined Benefit Plan Actuarial Gain Loss DefinedBenefitPlanActuarialGainLoss	-11500000
CY2017	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets	0.0700	pure
CY2017	us-gaap	Defined Benefit Plan Service Cost DefinedBenefitPlanServiceCost	1700000
CY2017	us-gaap	Depreciation Amortization And Accretion Net DepreciationAmortizationAndAccretionNet	385800000
CY2017	us-gaap	Defined Benefit Plan Benefit Obligation Benefits Paid DefinedBenefitPlanBenefitObligationBenefitsPaid	13100000
CY2017	us-gaap	Defined Benefit Plan Net Periodic Benefit Cost DefinedBenefitPlanNetPeriodicBenefitCost	2700000
CY2017	us-gaap	Depreciation Depreciation	121100000
CY2017	us-gaap	Derivative Instruments Gain Loss Reclassified From Accumulated Oci Into Income Effective Portion Net DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet	-5200000
CY2017	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	283600000
CY2017	us-gaap	Defined Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	0
CY2017	us-gaap	Direct Premiums Earned DirectPremiumsEarned	60400000
CY2017	us-gaap	Direct Premiums Written DirectPremiumsWritten	60700000
CY2017	us-gaap	Derivative Net Hedge Ineffectiveness Gain Loss DerivativeNetHedgeIneffectivenessGainLoss	-200000
CY2017	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	-0.437	pure
CY2017	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.64
CY2017	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.350	pure
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	0.034	pure
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	-0.042	pure
CY2017	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.014	pure
CY2017	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	72000000
CY2017	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.67
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Change In Enacted Tax Rate EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate	-0.092	pure
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Foreign Income Tax Rate Differential EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential	-0.130	pure
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.001	pure
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.640	pure
CY2017	us-gaap	Federal Income Tax Expense Benefit Continuing Operations FederalIncomeTaxExpenseBenefitContinuingOperations	-176400000
CY2017	us-gaap	Foreign Income Tax Expense Benefit Continuing Operations ForeignIncomeTaxExpenseBenefitContinuingOperations	11600000
CY2017	us-gaap	Goodwill Translation And Purchase Accounting Adjustments GoodwillTranslationAndPurchaseAccountingAdjustments	110900000
CY2017	us-gaap	Foreign Currency Transaction Gain Loss Unrealized ForeignCurrencyTransactionGainLossUnrealized	-3900000
CY2017	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	-3900000
CY2017	us-gaap	Gain Loss On Derivative Instruments Net Pretax GainLossOnDerivativeInstrumentsNetPretax	8300000
CY2017	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	304500000
CY2017	us-gaap	Gain Loss On Investments GainLossOnInvestments	100000
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	274100000
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	359800000
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	85700000
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	359800000
CY2017	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-157100000
CY2017	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	-33200000
CY2017	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	55800000
CY2017	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	126000000
CY2017	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	-15100000
CY2017	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	219300000
CY2017	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	12300000
CY2017	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	-46900000
CY2017	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	5000000
CY2017	us-gaap	Income Tax Reconciliation Tax Credits IncomeTaxReconciliationTaxCredits	230100000
CY2017	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	2000000
CY2017	us-gaap	Increase Decrease In Contract With Customer Liability IncreaseDecreaseInContractWithCustomerLiability	900000
CY2017	us-gaap	Goodwill Purchase Accounting Adjustments GoodwillPurchaseAccountingAdjustments	14700000
CY2017	us-gaap	Impairment Of Intangible Assets Finitelived ImpairmentOfIntangibleAssetsFinitelived	6200000
CY2017	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-400000
CY2017	us-gaap	Interest Expense InterestExpense	124100000
CY2017	us-gaap	Interest Expense Domestic Deposits InterestExpenseDomesticDeposits	64200000
CY2017	us-gaap	Increase Decrease In Reinsurance Payables IncreaseDecreaseInReinsurancePayables	166900000
CY2017	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	35300000
CY2017	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	13200000
CY2017	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	2000000	shares
CY2017	us-gaap	Interest Paid Net InterestPaidNet	124800000
CY2017	us-gaap	Labor And Related Expense LaborAndRelatedExpense	2747400000
CY2017	us-gaap	Minority Interest Decrease From Redemptions MinorityInterestDecreaseFromRedemptions	2100000
CY2017	us-gaap	Number Of Businesses Acquired NumberOfBusinessesAcquired	108	Entity
CY2017	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-511000000
CY2017	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-47800000
CY2017	us-gaap	Minority Interest Decrease From Distributions To Noncontrolling Interest Holders MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders	34400000
CY2017	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	854200000
CY2017	us-gaap	Net Income Loss NetIncomeLoss	481300000
CY2017	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	35600000
CY2017	us-gaap	Other Comprehensive Income Foreign Currency Transaction And Translation Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax	180900000
CY2017	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	-4200000
CY2017	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-4300000
CY2017	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax	15000000
CY2017	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax	16000000
CY2017	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax	4000000
CY2017	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	5000000
CY2017	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	181700000
CY2017	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-800000
CY2017	us-gaap	Operating Expenses OperatingExpenses	829100000
CY2017	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	2800000
CY2017	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax	5200000
CY2017	us-gaap	Operating Leases Rent Expense Net OperatingLeasesRentExpenseNet	137700000
CY2017	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Reclassification Adjustment From Aoci Realized Upon Sale Or Liquidation Before Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationReclassificationAdjustmentFromAOCIRealizedUponSaleOrLiquidationBeforeTax	0
CY2017	us-gaap	Payments For Previous Acquisition PaymentsForPreviousAcquisition	57900000
CY2017	us-gaap	Premiums Earned Net PremiumsEarnedNet	0
CY2017	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	5000000
CY2017	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	282700000
CY2017	us-gaap	Payments For Proceeds From Investments PaymentsForProceedsFromInvestments	8900000
CY2017	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	17700000
CY2017	us-gaap	Payments For Capital Improvements PaymentsForCapitalImprovements	129200000
CY2017	us-gaap	Payments To Minority Shareholders PaymentsToMinorityShareholders	35000000
CY2017	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	60400000
CY2017	us-gaap	Premiums Written Net PremiumsWrittenNet	0
CY2017	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	348000000
CY2017	us-gaap	Proceeds From Lines Of Credit ProceedsFromLinesOfCredit	3643000000
CY2017	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	600000
CY2017	us-gaap	Repayments Of Lines Of Credit RepaymentsOfLinesOfCredit	3731000000
CY2017	us-gaap	Profit Loss ProfitLoss	516900000
CY2017	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	6249000000
CY2017	us-gaap	Share Based Compensation ShareBasedCompensation	17300000
CY2017	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P5Y
CY2017	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P3Y4M20D
CY2017	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	33.11
CY2017	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	41100000
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0.028	pure
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.023	pure
CY2017	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1	P1Y9M
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod	400000	shares
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	476350	shares
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.272	pure
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	1700000	shares
CY2017	us-gaap	State And Local Income Tax Expense Benefit Continuing Operations StateAndLocalIncomeTaxExpenseBenefitContinuingOperations	7700000
CY2017	us-gaap	Stock Issued During Period Value Acquisitions StockIssuedDuringPeriodValueAcquisitions	60600000
CY2017	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice	44.48
CY2017	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice	56.87
CY2017	us-gaap	Stock Granted During Period Value Sharebased Compensation StockGrantedDuringPeriodValueSharebasedCompensation	17300000
CY2017	us-gaap	Stock Repurchased During Period Value StockRepurchasedDuringPeriodValue	17700000
CY2017	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	1300000	shares
CY2017	us-gaap	Stock Issued During Period Value Employee Stock Purchase Plan StockIssuedDuringPeriodValueEmployeeStockPurchasePlan	19300000
CY2017	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	1800000
CY2017	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	600000
CY2017	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	700000
CY2017	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	180100000	shares
CY2017	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	1600000
CY2017	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	3300000
CY2017	ajg	Amortization Of Deferred Compensation And Restricted Stock AmortizationOfDeferredCompensationAndRestrictedStock	33500000
CY2017	ajg	Lease Abandonment Charges LeaseAbandonmentCharges	13200000
CY2017	ajg	Earnout Payments For Acquisitions EarnoutPaymentsForAcquisitions	41700000
CY2017	ajg	Increase Decrease In Premiums And Fees Receivable IncreaseDecreaseInPremiumsAndFeesReceivable	47700000
CY2017	ajg	Payments To Acquire Businesses Net Of Cash And Restricted Cash Acquired PaymentsToAcquireBusinessesNetOfCashAndRestrictedCashAcquired	376100000
CY2017	ajg	Change In Estimated Acquisition Earnout Payables ChangeInEstimatedAcquisitionEarnoutPayables	30900000
CY2017	ajg	Net Change In Accrued Compensation And Other Accrued Liabilities NetChangeInAccruedCompensationAndOtherAccruedLiabilities	-69600000
CY2017	ajg	Deferred Compensation And Restricted Stock Expenses Benefit DeferredCompensationAndRestrictedStockExpensesBenefit	4800000
CY2017	ajg	Share Based Compensation Arrangement By Share Based Payment Award Options Exercised In Period Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodIntrinsicValue	33700000
CY2017	ajg	Business Acquisitions Pro Forma Net Income Loss To Controlling Interest BusinessAcquisitionsProFormaNetIncomeLossToControllingInterest	496400000
CY2017	ajg	Allowances For Estimated Policy Cancellations AllowancesForEstimatedPolicyCancellations	7400000
CY2017	ajg	Proceeds From Settlements On Terminated Interest Rate Swaps ProceedsFromSettlementsOnTerminatedInterestRateSwaps	8300000
CY2017	ajg	Income Tax Reconciliation Other Permanent Differences IncomeTaxReconciliationOtherPermanentDifferences	-10600000
CY2017	ajg	Business Combination Aggregate Earnout Obligation Maximum BusinessCombinationAggregateEarnoutObligationMaximum	567900000
CY2017	ajg	Net Proceeds From Sales Of Operations NetProceedsFromSalesOfOperations	3200000
CY2017	ajg	Cost Reimbursements CostReimbursements	136000000
CY2017	ajg	Business Combination Aggregate Earnout Obligation Recorded Maximum BusinessCombinationAggregateEarnoutObligationRecordedMaximum	264200000
CY2017	ajg	Income Tax Reconciliation Changes In Unrecognized Tax Benefits Related To Resolution Of Federal And State Audits Expiration Of Various Statutes Of Limitations And Other Items IncomeTaxReconciliationChangesInUnrecognizedTaxBenefitsRelatedToResolutionOfFederalAndStateAuditsExpirationOfVariousStatutesOfLimitationsAndOtherItems	-900000
CY2017	ajg	Contract With Customer Liability Additions ContractWithCustomerLiabilityAdditions	382900000
CY2017	ajg	Net Change In Accrued Compensation And Other Current Liabilities NetChangeInAccruedCompensationAndOtherCurrentLiabilities	-69600000
CY2017	ajg	Weighted Average Number Of Common And Common Equivalent Shares Outstanding WeightedAverageNumberOfCommonAndCommonEquivalentSharesOutstanding	182100000	shares
CY2017	ajg	Expected Period Of Return On Plan Assets ExpectedPeriodOfReturnOnPlanAssets	P10Y
CY2017	ajg	Effective Income Tax Rate Reconciliation Changes In Unrecognized Tax Benefits Related To Resolution Of Federal And State Audits Expiration Of Various Statutes Of Limitations And Other Items EffectiveIncomeTaxRateReconciliationChangesInUnrecognizedTaxBenefitsRelatedToResolutionOfFederalAndStateAuditsExpirationOfVariousStatutesOfLimitationsAndOtherItems	-0.003	pure
CY2017	ajg	Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Expected Long Term Return On Plan Assets DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationExpectedLongTermReturnOnPlanAssets	0.0700	pure
CY2017	ajg	Effective Income Tax Rate Reconciliation Other Permanent Differences EffectiveIncomeTaxRateReconciliationOtherPermanentDifferences	-0.029	pure
CY2017	ajg	Increase Decrease In Premiums And Fee Receivable IncreaseDecreaseInPremiumsAndFeeReceivable	47700000
CY2017	ajg	Revenue From Contract With Customer Before Reimbursements Excluding Assessed Tax RevenueFromContractWithCustomerBeforeReimbursementsExcludingAssessedTax	6113000000
CY2017	ajg	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested And Expected To Vest Outstanding Weighted Average Remaining Contractual Term SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm	P4Y7M20D
CY2017	ajg	Increase Decrease In Income Taxes Reconciliation Repatriation Of Foreign Earnings IncreaseDecreaseInIncomeTaxesReconciliationRepatriationOfForeignEarnings	36800000
CY2017	ajg	Increase Decrease In Effective Income Tax Rate Reconciliation Repatriation Of Foreign Earnings IncreaseDecreaseInEffectiveIncomeTaxRateReconciliationRepatriationOfForeignEarnings	0.102	pure
CY2018	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	1000000	shares
CY2018	us-gaap	Adjustment For Amortization AdjustmentForAmortization	291200000
CY2018	dei	Amendment Flag AmendmentFlag	false
CY2018	us-gaap	Amount Recognized In Net Periodic Benefit Cost And Other Comprehensive Income Loss Before Tax AmountRecognizedInNetPeriodicBenefitCostAndOtherComprehensiveIncomeLossBeforeTax	11300000
CY2018	us-gaap	Business Acquisition Pro Forma Earnings Per Share Basic BusinessAcquisitionProFormaEarningsPerShareBasic	3.53
CY2018	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	7125500000
CY2018	us-gaap	Business Combination Consideration Transferred Equity Interests Issued And Issuable BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable	54200000
CY2018	us-gaap	Business Acquisition Equity Interests Issued Or Issuable Number Of Shares Issued BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued	826000	shares
CY2018	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	9200000
CY2018	us-gaap	Assumed Premiums Earned AssumedPremiumsEarned	4600000
CY2018	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	4700000
CY2018	us-gaap	Business Combination Separately Recognized Transactions Additional Disclosures Acquisition Cost Expensed BusinessCombinationSeparatelyRecognizedTransactionsAdditionalDisclosuresAcquisitionCostExpensed	18800000
CY2018	us-gaap	Business Acquisition Pro Forma Earnings Per Share Diluted BusinessAcquisitionProFormaEarningsPerShareDiluted	3.46
CY2018	us-gaap	Ceded Premiums Earned CededPremiumsEarned	57800000
CY2018	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	40400000
CY2018	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	-68200000
CY2018	us-gaap	Ceded Premiums Written CededPremiumsWritten	62300000
CY2018	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.64
CY2018	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	411900000
CY2018	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	452300000
CY2018	us-gaap	Contract With Customer Liability Revenue Recognized ContractWithCustomerLiabilityRevenueRecognized	373500000
CY2018	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	60700000
CY2018	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	15400000
CY2018	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-29600000
CY2018	us-gaap	Contract With Customer Liability Increase Decrease For Contract Acquired In Business Combination ContractWithCustomerLiabilityIncreaseDecreaseForContractAcquiredInBusinessCombination	18500000
CY2018	us-gaap	Cost Of Goods And Services Sold CostOfGoodsAndServicesSold	1816000000
CY2018	us-gaap	Costs And Expenses CostsAndExpenses	6454600000
CY2018	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2018	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-214000000
CY2018	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-29000000
CY2018	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate	0.0350	pure
CY2018	us-gaap	Defined Benefit Plan Interest Cost DefinedBenefitPlanInterestCost	9300000
CY2018	us-gaap	Defined Benefit Plan Actual Return On Plan Assets DefinedBenefitPlanActualReturnOnPlanAssets	-15400000
CY2018	us-gaap	Defined Benefit Plan Amortization Of Gains Losses DefinedBenefitPlanAmortizationOfGainsLosses	-4900000
CY2018	us-gaap	Defined Benefit Plan Contributions By Employer DefinedBenefitPlanContributionsByEmployer	30000000
CY2018	us-gaap	Defined Benefit Plan Expected Return On Plan Assets DefinedBenefitPlanExpectedReturnOnPlanAssets	16000000
CY2018	us-gaap	Defined Benefit Plan Actuarial Gain Loss DefinedBenefitPlanActuarialGainLoss	14300000
CY2018	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets	0.0700	pure
CY2018	us-gaap	Defined Benefit Plan Service Cost DefinedBenefitPlanServiceCost	800000
CY2018	us-gaap	Depreciation Amortization And Accretion Net DepreciationAmortizationAndAccretionNet	419000000
CY2018	us-gaap	Defined Benefit Plan Benefit Obligation Benefits Paid DefinedBenefitPlanBenefitObligationBenefitsPaid	14000000
CY2018	us-gaap	Defined Benefit Plan Net Periodic Benefit Cost DefinedBenefitPlanNetPeriodicBenefitCost	-1000000
CY2018	us-gaap	Depreciation Depreciation	127800000
CY2018	us-gaap	Derivative Instruments Gain Loss Reclassified From Accumulated Oci Into Income Effective Portion Net DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet	5700000
CY2018	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	303300000
CY2018	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2018	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2018
CY2018	dei	Document Type DocumentType	10-K
CY2018	us-gaap	Defined Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	30000000
CY2018	us-gaap	Direct Premiums Earned DirectPremiumsEarned	53200000
CY2018	us-gaap	Direct Premiums Written DirectPremiumsWritten	57600000
CY2018	us-gaap	Derivative Net Hedge Ineffectiveness Gain Loss DerivativeNetHedgeIneffectivenessGainLoss	-600000
CY2018	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	-0.410	pure
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	3.40
CY2018	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210	pure
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	-0.046	pure
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	-0.031	pure
CY2018	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.018	pure
CY2018	dei	Entity Central Index Key EntityCentralIndexKey	0000354190
CY2018	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	Yes
CY2018	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	-85000000
CY2018	dei	Entity Registrant Name EntityRegistrantName	GALLAGHER ARTHUR J & CO
CY2018	dei	Entity Shell Company EntityShellCompany	false
CY2018	dei	Entity Small Business EntitySmallBusiness	false
CY2018	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2018	dei	Document Period End Date DocumentPeriodEndDate	2018-12-31
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	3.47
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Foreign Income Tax Rate Differential EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential	-0.031	pure
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.528	pure
CY2018	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2018	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
CY2018	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
CY2018	us-gaap	Federal Income Tax Expense Benefit Continuing Operations FederalIncomeTaxExpenseBenefitContinuingOperations	-214000000
CY2018	us-gaap	Foreign Income Tax Expense Benefit Continuing Operations ForeignIncomeTaxExpenseBenefitContinuingOperations	31100000
CY2018	us-gaap	Goodwill Translation And Purchase Accounting Adjustments GoodwillTranslationAndPurchaseAccountingAdjustments	-123700000
CY2018	us-gaap	Foreign Currency Transaction Gain Loss Unrealized ForeignCurrencyTransactionGainLossUnrealized	2900000
CY2018	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	2900000
CY2018	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	584600000
CY2018	us-gaap	Gain Loss On Investments GainLossOnInvestments	8400000
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	337600000
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	479400000
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	141800000
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	479400000
CY2018	us-gaap	Income Tax Credits And Adjustments IncomeTaxCreditsAndAdjustments	108000000
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-196500000
CY2018	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	68100000
CY2018	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	100700000
CY2018	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	-15000000
CY2018	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	216000000
CY2018	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	-22000000
CY2018	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	-14800000
CY2018	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	8500000
CY2018	us-gaap	Income Tax Reconciliation Tax Credits IncomeTaxReconciliationTaxCredits	252900000
CY2018	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	-46000000
CY2018	us-gaap	Increase Decrease In Contract With Customer Liability IncreaseDecreaseInContractWithCustomerLiability	18400000
CY2018	us-gaap	Goodwill Purchase Accounting Adjustments GoodwillPurchaseAccountingAdjustments	-100000
CY2018	us-gaap	Impairment Of Intangible Assets Finitelived ImpairmentOfIntangibleAssetsFinitelived	10600000
CY2018	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	100000
CY2018	us-gaap	Interest Expense InterestExpense	138400000
CY2018	us-gaap	Interest Expense Domestic Deposits InterestExpenseDomesticDeposits	65800000
CY2018	us-gaap	Increase Decrease In Reinsurance Payables IncreaseDecreaseInReinsurancePayables	819700000
CY2018	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	134700000
CY2018	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	22000000
CY2018	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	3500000	shares
CY2018	us-gaap	Interest Paid Net InterestPaidNet	139200000
CY2018	us-gaap	Labor And Related Expense LaborAndRelatedExpense	3026300000
CY2018	us-gaap	Minority Interest Decrease From Redemptions MinorityInterestDecreaseFromRedemptions	700000
CY2018	us-gaap	Number Of Businesses Acquired NumberOfBusinessesAcquired	112	Entity
CY2018	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	4900000
CY2018	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	-199700000
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-17200000
CY2018	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-910300000
CY2018	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	162000000
CY2018	us-gaap	Minority Interest Decrease From Distributions To Noncontrolling Interest Holders MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders	38000000
CY2018	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	765100000
CY2018	us-gaap	Net Income Loss NetIncomeLoss	633500000
CY2018	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	42400000
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentBeforeTax	12300000
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	10300000
CY2018	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax	-15700000
CY2018	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax	-15600000
CY2018	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax	-5600000
CY2018	us-gaap	Number Of Reportable Segments NumberOfReportableSegments	3	Segment
CY2018	us-gaap	Open Tax Year OpenTaxYear	2011 2012
CY2018	us-gaap	Operating Expenses OperatingExpenses	903700000
CY2018	us-gaap	Other Comprehensive Income Foreign Currency Transaction And Translation Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax	-197700000
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	6200000
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax	5700000
CY2018	us-gaap	Operating Leases Rent Expense Net OperatingLeasesRentExpenseNet	140000000
CY2018	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Reclassification Adjustment From Aoci Realized Upon Sale Or Liquidation Before Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationReclassificationAdjustmentFromAOCIRealizedUponSaleOrLiquidationBeforeTax	0
CY2018	us-gaap	Payments For Previous Acquisition PaymentsForPreviousAcquisition	64600000
CY2018	us-gaap	Premiums Earned Net PremiumsEarnedNet	0
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	4900000
CY2018	us-gaap	Payments Of Debt Issuance Costs PaymentsOfDebtIssuanceCosts	1300000
CY2018	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	301800000
CY2018	us-gaap	Payments For Proceeds From Investments PaymentsForProceedsFromInvestments	15600000
CY2018	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	11300000
CY2018	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	6934000000
CY2018	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	81900000
CY2018	us-gaap	Payments For Capital Improvements PaymentsForCapitalImprovements	124400000
CY2018	us-gaap	Payments To Acquire Businesses Gross PaymentsToAcquireBusinessesGross	792200000
CY2018	us-gaap	Payments To Minority Shareholders PaymentsToMinorityShareholders	54200000
CY2018	us-gaap	Premiums Written Net PremiumsWrittenNet	0
CY2018	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	400000000
CY2018	us-gaap	Proceeds From Lines Of Credit ProceedsFromLinesOfCredit	3075000000
CY2018	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	32900000
CY2018	us-gaap	Repayments Of Lines Of Credit RepaymentsOfLinesOfCredit	3000000000
CY2018	us-gaap	Profit Loss ProfitLoss	675900000
CY2018	us-gaap	Share Based Compensation ShareBasedCompensation	13700000
CY2018	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P5Y6M
CY2018	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P3Y10M9D
CY2018	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	37.85
CY2018	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	58600000
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0.023	pure
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.027	pure
CY2018	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1	P1Y9M29D
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod	400000	shares
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	439100	shares
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.151	pure
CY2018	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	1400000
CY2018	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	1300000	shares
CY2018	dei	Trading Symbol TradingSymbol	AJG
CY2018	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice	49.23
CY2018	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice	70.74
CY2018	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Lower Range Limit ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit	35.71
CY2018	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Upper Range Limit ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit	70.74
CY2018	us-gaap	State And Local Income Tax Expense Benefit Continuing Operations StateAndLocalIncomeTaxExpenseBenefitContinuingOperations	-13600000
CY2018	us-gaap	Stock Issued During Period Value Acquisitions StockIssuedDuringPeriodValueAcquisitions	61600000
CY2018	us-gaap	Stock Granted During Period Value Sharebased Compensation StockGrantedDuringPeriodValueSharebasedCompensation	13700000
CY2018	us-gaap	Stock Repurchased During Period Value StockRepurchasedDuringPeriodValue	11300000
CY2018	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	1600000	shares
CY2018	us-gaap	Stock Issued During Period Value Employee Stock Purchase Plan StockIssuedDuringPeriodValueEmployeeStockPurchasePlan	23300000
CY2018	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	400000
CY2018	us-gaap	Variable Interest Entity Ownership Percentage VariableInterestEntityOwnershipPercentage	0.50	pure
CY2018	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	182700000	shares
CY2018	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	1700000
CY2018	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	900000
CY2018	us-gaap	Use Of Estimates UseOfEstimates	<div> <p style="MARGIN-BOTTOM: 0px; MARGIN-TOP: 0px"><font style="FONT-FAMILY: Times New Roman" size="2"><b>Use of Estimates</b></font></p> <p style="MARGIN-BOTTOM: 0px; MARGIN-TOP: 6px"><font style="FONT-FAMILY: Times New Roman" size="2">The preparation of our consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. These accounting principles require us to make estimates and assumptions that affect the reported amounts of assets and liabilities and revenues and expenses, and the disclosure of contingent assets and liabilities at the date of our consolidated financial statements. We are also required to make certain judgments and estimates that affect the disclosed and recorded amounts of revenues and expenses related to the impact of the adoption of and accounting under Topic 606. We periodically evaluate our estimates and assumptions, including those relating to the valuation of goodwill and other intangible assets, investments (including our IRC Section 45 investments), income taxes, revenue recognition, deferred costs, stock-based compensation, claims handling obligations, retirement plans, litigation and contingencies. We base our estimates on historical experience and various assumptions that we believe to be reasonable based on specific circumstances. Such estimates and assumptions could change in the future as more information becomes known, which could impact the amounts reported and disclosed herein.</font></p> </div>
CY2018	ajg	Number Of Countries In Which Company Does Business Through Network Of Correspondent Brokers And Consultants NumberOfCountriesInWhichCompanyDoesBusinessThroughNetworkOfCorrespondentBrokersAndConsultants	150	Country
CY2018	ajg	Number Of Countries In Which Company Has Operations NumberOfCountriesInWhichCompanyHasOperations	35	Country
CY2018	ajg	Amortization Of Deferred Compensation And Restricted Stock AmortizationOfDeferredCompensationAndRestrictedStock	41600000
CY2018	ajg	Earnout Payments For Acquisitions EarnoutPaymentsForAcquisitions	62100000
CY2018	ajg	Payments To Acquire Businesses Net Of Cash And Restricted Cash Acquired PaymentsToAcquireBusinessesNetOfCashAndRestrictedCashAcquired	784800000
CY2018	ajg	Change In Estimated Acquisition Earnout Payables ChangeInEstimatedAcquisitionEarnoutPayables	9600000
CY2018	ajg	Net Change In Accrued Compensation And Other Accrued Liabilities NetChangeInAccruedCompensationAndOtherAccruedLiabilities	-44900000
CY2018	ajg	Deferred Compensation And Restricted Stock Expenses Benefit DeferredCompensationAndRestrictedStockExpensesBenefit	15800000
CY2018	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year Two AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearTwo	1500000
CY2018	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year Three AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThree	200000
CY2018	ajg	Share Based Compensation Arrangement By Share Based Payment Award Options Exercised In Period Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodIntrinsicValue	54200000
CY2018	ajg	Business Acquisitions Pro Forma Net Income Loss To Controlling Interest BusinessAcquisitionsProFormaNetIncomeLossToControllingInterest	646100000
CY2018	ajg	Allowances For Estimated Policy Cancellations AllowancesForEstimatedPolicyCancellations	7800000
CY2018	ajg	Proceeds From Settlements On Terminated Interest Rate Swaps ProceedsFromSettlementsOnTerminatedInterestRateSwaps	2900000
CY2018	ajg	Income Tax Reconciliation Other Permanent Differences IncomeTaxReconciliationOtherPermanentDifferences	900000
CY2018	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments AmountOfCommitmentExpirationOffBalanceSheetCommitments	19900000
CY2018	ajg	Business Combination Aggregate Earnout Obligation Maximum BusinessCombinationAggregateEarnoutObligationMaximum	558100000
CY2018	ajg	Net Proceeds From Sales Of Operations NetProceedsFromSalesOfOperations	14500000
CY2018	ajg	Deferred Equity Participation Plan Distributions To Key Executives Age DeferredEquityParticipationPlanDistributionsToKeyExecutivesAge	Age 62 (or the one-year anniversary of the date of the grant for participants over the age of 61 as of the grant date) or upon or after their actual retirement.
CY2018	ajg	Maturity Period Of Short Term Investments MaturityPeriodOfShortTermInvestments	90 days or less
CY2018	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year Thereafter AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThereafter	17600000
CY2018	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year One AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearOne	200000
CY2018	ajg	Cost Reimbursements CostReimbursements	141600000
CY2018	ajg	Business Combination Aggregate Earnout Obligation Recorded Maximum BusinessCombinationAggregateEarnoutObligationRecordedMaximum	258800000
CY2018	ajg	Income Tax Reconciliation Changes In Unrecognized Tax Benefits Related To Resolution Of Federal And State Audits Expiration Of Various Statutes Of Limitations And Other Items IncomeTaxReconciliationChangesInUnrecognizedTaxBenefitsRelatedToResolutionOfFederalAndStateAuditsExpirationOfVariousStatutesOfLimitationsAndOtherItems	-200000
CY2018	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year Four AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFour	200000
CY2018	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year Five AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFive	200000
CY2018	ajg	Recorded Earn Out Payable RecordedEarnOutPayable	94000000
CY2018	ajg	Contract With Customer Liability Additions ContractWithCustomerLiabilityAdditions	382100000
CY2018	ajg	Weighted Average Number Of Common And Common Equivalent Shares Outstanding WeightedAverageNumberOfCommonAndCommonEquivalentSharesOutstanding	186200000	shares
CY2018	ajg	Deferred Equity Participation Sub Plan Distributions Requisite Service Description DeferredEquityParticipationSubPlanDistributionsRequisiteServiceDescription	We made awards under sub-plans of the DEPP for certain production staff, which generally provide for vesting and/or distributions no sooner than five years from the date of awards, although certain awards vest and/or distribute after earlier of fifteen years or the participant reaching age 65.
CY2018	ajg	Deferred Equity Participation Sub Plan Distributions To Key Executives Age DeferredEquityParticipationSubPlanDistributionsToKeyExecutivesAge	Age 65
CY2018	ajg	Description Of Contracts Renewal Period DescriptionOfContractsRenewalPeriod	One year or less
CY2018	ajg	Insurance Contracts Premium Financing Terms InsuranceContractsPremiumFinancingTerms	Premium financing contracts are structured to minimize potential bad debt expense to us. Such receivables are generally considered delinquent after seven days of the payment due date. In normal course, insurance policies are cancelled within one month of the contractual payment due date if the payment remains delinquent.
CY2018	ajg	Number Of Employees NumberOfEmployees	2000	Employees
CY2018	ajg	Collateralized Delinquency Receivables Period CollateralizedDelinquencyReceivablesPeriod	P7D
CY2018	ajg	Weighted Average Period WeightedAveragePeriod	P4Y
CY2018	ajg	Expected Period Of Return On Plan Assets ExpectedPeriodOfReturnOnPlanAssets	P10Y
CY2018	ajg	Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Expected Long Term Return On Plan Assets DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationExpectedLongTermReturnOnPlanAssets	0.0700	pure
CY2018	ajg	Effective Income Tax Rate Reconciliation Other Permanent Differences EffectiveIncomeTaxRateReconciliationOtherPermanentDifferences	0.002	pure
CY2018	ajg	Percentage Of Commissions And Fee Revenues Recongized On Effective Date Of Insurance Contract PercentageOfCommissionsAndFeeRevenuesRecongizedOnEffectiveDateOfInsuranceContract	0.80	pure
CY2018	ajg	Percentage Of Commissions And Fee Revenues Recongized In First Three Months Of Insurance Contract PercentageOfCommissionsAndFeeRevenuesRecongizedInFirstThreeMonthsOfInsuranceContract	0.15	pure
CY2018	ajg	Percentage Of Commissions And Fee Revenues Recongized After First Three Months Of Insurance Contract PercentageOfCommissionsAndFeeRevenuesRecongizedAfterFirstThreeMonthsOfInsuranceContract	0.05	pure
CY2018	ajg	Increase Decrease In Premiums And Fee Receivable IncreaseDecreaseInPremiumsAndFeeReceivable	783100000
CY2018	ajg	Revenue From Contract With Customer Before Reimbursements Excluding Assessed Tax RevenueFromContractWithCustomerBeforeReimbursementsExcludingAssessedTax	6792400000
CY2018	ajg	Sharebased Compensation Arrangement By Sharebased Payment Award Options Nonvested And Expected To Vest Outstanding Weighted Average Remaining Contractual Term SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsNonvestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm	P4Y5M15D
CY2018	ajg	Increase Decrease In Income Taxes Reconciliation Repatriation Of Foreign Earnings IncreaseDecreaseInIncomeTaxesReconciliationRepatriationOfForeignEarnings	-1800000
CY2018	ajg	Increase Decrease In Effective Income Tax Rate Reconciliation Repatriation Of Foreign Earnings IncreaseDecreaseInEffectiveIncomeTaxRateReconciliationRepatriationOfForeignEarnings	-0.004	pure
CY2016	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	5900000	shares
CY2016	us-gaap	Adjustment For Amortization AdjustmentForAmortization	247200000
CY2016	us-gaap	Amount Recognized In Net Periodic Benefit Cost And Other Comprehensive Income Loss Before Tax AmountRecognizedInNetPeriodicBenefitCostAndOtherComprehensiveIncomeLossBeforeTax	-900000
CY2016	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	15200000
CY2016	us-gaap	Assumed Premiums Earned AssumedPremiumsEarned	4900000
CY2016	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	5200000
CY2016	us-gaap	Business Combination Separately Recognized Transactions Additional Disclosures Acquisition Cost Expensed BusinessCombinationSeparatelyRecognizedTransactionsAdditionalDisclosuresAcquisitionCostExpensed	16900000
CY2016	us-gaap	Ceded Premiums Earned CededPremiumsEarned	74500000
CY2016	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	37900000
CY2016	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	45100000
CY2016	us-gaap	Ceded Premiums Written CededPremiumsWritten	77000000
CY2016	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.52
CY2016	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	158300000
CY2016	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	196200000
CY2016	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	40200000
CY2016	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	20700000
CY2016	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	7200000
CY2016	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-17800000
CY2016	us-gaap	Cost Of Goods And Services Sold CostOfGoodsAndServicesSold	1408600000
CY2016	us-gaap	Costs And Expenses CostsAndExpenses	5346900000
CY2016	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-146700000
CY2016	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-300000
CY2016	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate	0.0425	pure
CY2016	us-gaap	Defined Benefit Plan Interest Cost DefinedBenefitPlanInterestCost	10800000
CY2016	us-gaap	Defined Benefit Plan Amortization Of Gains Losses DefinedBenefitPlanAmortizationOfGainsLosses	-5300000
CY2016	us-gaap	Defined Benefit Plan Contributions By Employer DefinedBenefitPlanContributionsByEmployer	0
CY2016	us-gaap	Defined Benefit Plan Expected Return On Plan Assets DefinedBenefitPlanExpectedReturnOnPlanAssets	14600000
CY2016	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets	0.0725	pure
CY2016	us-gaap	Defined Benefit Plan Service Cost DefinedBenefitPlanServiceCost	1500000
CY2016	us-gaap	Interest Expense InterestExpense	109800000
CY2016	us-gaap	Interest Expense Domestic Deposits InterestExpenseDomesticDeposits	110700000
CY2016	us-gaap	Increase Decrease In Reinsurance Payables IncreaseDecreaseInReinsurancePayables	770000000
CY2016	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	45500000
CY2016	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	27500000
CY2016	us-gaap	Depreciation Amortization And Accretion Net DepreciationAmortizationAndAccretionNet	350800000
CY2016	us-gaap	Defined Benefit Plan Net Periodic Benefit Cost DefinedBenefitPlanNetPeriodicBenefitCost	3000000
CY2016	us-gaap	Depreciation Depreciation	103600000
CY2016	us-gaap	Derivative Instruments Gain Loss Reclassified From Accumulated Oci Into Income Effective Portion Net DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet	-8200000
CY2016	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	272500000
CY2016	us-gaap	Defined Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	0
CY2016	us-gaap	Direct Premiums Earned DirectPremiumsEarned	69600000
CY2016	us-gaap	Direct Premiums Written DirectPremiumsWritten	71800000
CY2016	us-gaap	Derivative Net Hedge Ineffectiveness Gain Loss DerivativeNetHedgeIneffectivenessGainLoss	1600000
CY2016	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	-0.290	pure
CY2016	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.22
CY2016	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.350	pure
CY2016	us-gaap	Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	0.042	pure
CY2016	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.013	pure
CY2016	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	-107600000
CY2016	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.23
CY2016	us-gaap	Effective Income Tax Rate Reconciliation Change In Enacted Tax Rate EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate	-0.004	pure
CY2016	us-gaap	Effective Income Tax Rate Reconciliation Foreign Income Tax Rate Differential EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential	-0.099	pure
CY2016	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.001	pure
CY2016	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.582	pure
CY2016	us-gaap	Federal Income Tax Expense Benefit Continuing Operations FederalIncomeTaxExpenseBenefitContinuingOperations	-106500000
CY2016	us-gaap	Foreign Income Tax Expense Benefit Continuing Operations ForeignIncomeTaxExpenseBenefitContinuingOperations	2900000
CY2016	us-gaap	Foreign Currency Transaction Gain Loss Unrealized ForeignCurrencyTransactionGainLossUnrealized	5300000
CY2016	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	5300000
CY2016	us-gaap	Gain Loss On Investments GainLossOnInvestments	6500000
CY2016	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	335700000
CY2016	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	333600000
CY2016	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	-2100000
CY2016	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	333600000
CY2016	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-96700000
CY2016	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	-1500000
CY2016	us-gaap	Income Taxes Paid Net IncomeTaxesPaidNet	66100000
CY2016	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	116700000
CY2016	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	166100000
CY2016	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	14000000
CY2016	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	-33100000
CY2016	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	4500000
CY2016	us-gaap	Income Tax Reconciliation Tax Credits IncomeTaxReconciliationTaxCredits	194400000
CY2016	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	-10800000
CY2016	us-gaap	Increase Decrease In Contract With Customer Liability IncreaseDecreaseInContractWithCustomerLiability	15100000
CY2016	us-gaap	Impairment Of Intangible Assets Finitelived ImpairmentOfIntangibleAssetsFinitelived	1800000
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CY2016	us-gaap	Minority Interest Decrease From Redemptions MinorityInterestDecreaseFromRedemptions	-8300000
CY2016	us-gaap	Number Of Businesses Acquired NumberOfBusinessesAcquired	101	Entity
CY2016	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-485300000
CY2016	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-11600000
CY2016	us-gaap	Minority Interest Decrease From Distributions To Noncontrolling Interest Holders MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders	34100000
CY2016	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	649600000
CY2016	us-gaap	Net Income Loss NetIncomeLoss	396800000
CY2016	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	33500000
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CY2016	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	4400000
CY2016	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax	-11500000
CY2016	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax	-4900000
CY2016	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax	-3200000
CY2016	us-gaap	Other Comprehensive Income Loss Amortization Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Prior Service Cost Credit Before Tax OtherComprehensiveIncomeLossAmortizationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetPriorServiceCostCreditBeforeTax	5300000
CY2016	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	-220400000
CY2016	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-1400000
CY2016	us-gaap	Operating Expenses OperatingExpenses	776300000
CY2016	us-gaap	Other Comprehensive Income Foreign Currency Transaction And Translation Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax	-224800000
CY2016	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	-2900000
CY2016	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax	8200000
CY2016	us-gaap	Operating Leases Rent Expense Net OperatingLeasesRentExpenseNet	134200000
CY2016	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Reclassification Adjustment From Aoci Realized Upon Sale Or Liquidation Before Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationReclassificationAdjustmentFromAOCIRealizedUponSaleOrLiquidationBeforeTax	0
CY2016	us-gaap	Payments For Previous Acquisition PaymentsForPreviousAcquisition	22800000
CY2016	us-gaap	Premiums Earned Net PremiumsEarnedNet	0
CY2016	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	5300000
CY2016	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	272200000
CY2016	us-gaap	Payments For Proceeds From Investments PaymentsForProceedsFromInvestments	31900000
CY2016	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	101000000
CY2016	us-gaap	Payments For Capital Improvements PaymentsForCapitalImprovements	217800000
CY2016	us-gaap	Payments To Minority Shareholders PaymentsToMinorityShareholders	41800000
CY2016	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	45600000
CY2016	us-gaap	Premiums Written Net PremiumsWrittenNet	0
CY2016	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	326000000
CY2016	us-gaap	Proceeds From Lines Of Credit ProceedsFromLinesOfCredit	2740000000
CY2016	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	-12200000
CY2016	us-gaap	Repayments Of Lines Of Credit RepaymentsOfLinesOfCredit	2657000000
CY2016	us-gaap	Profit Loss ProfitLoss	430300000
CY2016	us-gaap	Revenue From Contract With Customer Excluding Assessed Tax RevenueFromContractWithCustomerExcludingAssessedTax	5680500000
CY2016	us-gaap	Share Based Compensation ShareBasedCompensation	14700000
CY2016	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P5Y6M
CY2016	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	29700000
CY2016	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0.030	pure
CY2016	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.016	pure
CY2016	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	479167	shares
CY2016	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.277	pure
CY2016	us-gaap	State And Local Income Tax Expense Benefit Continuing Operations StateAndLocalIncomeTaxExpenseBenefitContinuingOperations	6900000
CY2016	us-gaap	Stock Issued During Period Value Acquisitions StockIssuedDuringPeriodValueAcquisitions	91600000
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CY2016	us-gaap	Stock Repurchased During Period Value StockRepurchasedDuringPeriodValue	101000000
CY2016	us-gaap	Stock Issued During Period Value Employee Stock Purchase Plan StockIssuedDuringPeriodValueEmployeeStockPurchasePlan	15900000
CY2016	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	177600000	shares
CY2016	ajg	Amortization Of Deferred Compensation And Restricted Stock AmortizationOfDeferredCompensationAndRestrictedStock	28500000
CY2016	ajg	Earnout Payments For Acquisitions EarnoutPaymentsForAcquisitions	45500000
CY2016	ajg	Increase Decrease In Premiums And Fees Receivable IncreaseDecreaseInPremiumsAndFeesReceivable	777200000
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CY2016	ajg	Net Change In Accrued Compensation And Other Accrued Liabilities NetChangeInAccruedCompensationAndOtherAccruedLiabilities	-69800000
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CY2016	ajg	Tax Expense From Issuance Of Common Stock TaxExpenseFromIssuanceOfCommonStock	6500000
CY2016	ajg	Share Based Compensation Arrangement By Share Based Payment Award Options Exercised In Period Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodIntrinsicValue	19300000
CY2016	ajg	Income Tax Reconciliation Other Permanent Differences IncomeTaxReconciliationOtherPermanentDifferences	-4800000
CY2016	ajg	Net Proceeds From Sales Of Operations NetProceedsFromSalesOfOperations	7800000
CY2016	ajg	Tax Impact From Issuance Of Common Stock TaxImpactFromIssuanceOfCommonStock	6500000
CY2016	ajg	Cost Reimbursements CostReimbursements	132100000
CY2016	ajg	Income Tax Reconciliation Changes In Unrecognized Tax Benefits Related To Resolution Of Federal And State Audits Expiration Of Various Statutes Of Limitations And Other Items IncomeTaxReconciliationChangesInUnrecognizedTaxBenefitsRelatedToResolutionOfFederalAndStateAuditsExpirationOfVariousStatutesOfLimitationsAndOtherItems	2200000
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CY2016	ajg	Weighted Average Number Of Common And Common Equivalent Shares Outstanding WeightedAverageNumberOfCommonAndCommonEquivalentSharesOutstanding	178400000	shares
CY2016	ajg	Effective Income Tax Rate Reconciliation Changes In Unrecognized Tax Benefits Related To Resolution Of Federal And State Audits Expiration Of Various Statutes Of Limitations And Other Items EffectiveIncomeTaxRateReconciliationChangesInUnrecognizedTaxBenefitsRelatedToResolutionOfFederalAndStateAuditsExpirationOfVariousStatutesOfLimitationsAndOtherItems	0.007	pure
CY2016	ajg	Effective Income Tax Rate Reconciliation Other Permanent Differences EffectiveIncomeTaxRateReconciliationOtherPermanentDifferences	-0.014	pure
CY2016	ajg	Increase Decrease In Premiums And Fee Receivable IncreaseDecreaseInPremiumsAndFeeReceivable	777200000
CY2016	ajg	Revenue From Contract With Customer Before Reimbursements Excluding Assessed Tax RevenueFromContractWithCustomerBeforeReimbursementsExcludingAssessedTax	5548400000
	us-gaap	Number Of Businesses Acquired NumberOfBusinessesAcquired	507	Entity
CY2017Q1	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1446800000
CY2017Q1	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	199600000
CY2017Q1	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	1.27
CY2017Q1	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	1.28
CY2017Q1	us-gaap	Net Income Loss NetIncomeLoss	228800000
CY2017Q1	us-gaap	Revenues Revenues	1646400000
CY2018Q1	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1595400000
CY2018Q1	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	242300000
CY2018Q1	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	1.48
CY2018Q1	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	1.51
CY2017Q2	us-gaap	Revenues Revenues	1489500000
CY2018Q2	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1556800000
CY2018Q2	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	103600000
CY2018Q2	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.62
CY2018Q1	us-gaap	Net Income Loss NetIncomeLoss	273700000
CY2018Q1	us-gaap	Revenues Revenues	1837700000
CY2017Q2	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1435400000
CY2017Q2	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	54100000
CY2017Q2	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.39
CY2017Q2	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.39
CY2017Q2	us-gaap	Net Income Loss NetIncomeLoss	70000000
CY2018Q2	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.63
CY2018Q2	us-gaap	Net Income Loss NetIncomeLoss	114900000
CY2018Q2	us-gaap	Revenues Revenues	1660400000
CY2017Q3	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1516800000
CY2017Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	76900000
CY2017Q3	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.61
CY2017Q3	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.61
CY2017Q3	us-gaap	Net Income Loss NetIncomeLoss	111000000
CY2017Q3	us-gaap	Revenues Revenues	1593700000
CY2018Q3	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1688200000
CY2018Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	90300000
CY2018Q3	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.68
CY2018Q3	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.70
CY2018Q3	us-gaap	Net Income Loss NetIncomeLoss	127600000
CY2018Q3	us-gaap	Revenues Revenues	1778500000
CY2017Q4	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1490200000
CY2017Q4	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	29200000
CY2017Q4	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.39
CY2017Q4	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.39
CY2017Q4	us-gaap	Net Income Loss NetIncomeLoss	71500000
CY2017Q4	us-gaap	Revenues Revenues	1519400000
CY2018Q4	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1614200000
CY2018Q4	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	43200000
CY2018Q4	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.63
CY2018Q4	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.64
CY2018Q4	us-gaap	Net Income Loss NetIncomeLoss	117300000
CY2018Q4	us-gaap	Revenues Revenues	1657400000

Files In Submission

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Arthur J. Gallagher & Co. Stock $ajg

2018 Q4 Form 10-K Financial Statement

#000119312519032304 Filed on February 08, 2019

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$AJG Arthur J. Gallagher & Co. Stock $ajg

2018 Q4 Form 10-K Financial Statement

#000119312519032304 Filed on February 08, 2019

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$AJG
Arthur J. Gallagher & Co. Stock $ajg