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

$ajg Overview Financials Valuation SEC Filings Company Website

2017 Form 10-K Financial Statement

#000119312518038261 Filed on February 12, 2018

Income Statement

Concept	2017	2016 Q4	2016 Q3
Revenue	$6.160B	$1.385B	$1.482B
YoY Change	10.1%	3.75%	1.89%
Cost Of Revenue	$1.636B	$1.119B	$1.076B
YoY Change	16.14%	17.78%	5.13%
Gross Profit	$4.524B	$351.6M	$406.0M
YoY Change	8.06%	-8.6%	-5.8%
Gross Profit Margin	73.44%	25.39%	27.39%
Selling, General & Admin
YoY Change
% of Gross Profit
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$121.1M	$89.30M	$25.70M
YoY Change	16.89%	-4.8%	7.98%
% of Gross Profit	2.68%	25.4%	6.33%
Operating Expenses	$829.1M	$277.8M	$189.6M
YoY Change	6.8%	-15.95%	-8.89%
Operating Profit	$3.695B	$73.80M	$216.4M
YoY Change	8.35%	36.16%	-2.92%
Interest Expense	$124.1M	-$28.30M	$28.50M
YoY Change	13.02%	9.69%	11.33%
% of Operating Profit	3.36%	-38.35%	13.17%
Other Income/Expense, Net
YoY Change
Pretax Income	$359.8M	$68.80M	$94.90M
YoY Change	7.85%	142.25%	-10.22%
Income Tax	-$157.1M	-$40.80M	-$35.50M
% Of Pretax Income	-43.66%	-59.3%	-37.41%
Net Earnings	$481.3M	$95.10M	$122.8M
YoY Change	21.3%	52.65%	-7.88%
Net Earnings / Revenue	7.81%	6.87%	8.28%
Basic Earnings Per Share	$2.67		$0.69
Diluted Earnings Per Share	$2.64	$433.0K	$0.69
COMMON SHARES
Basic Shares Outstanding	180.1M shares		177.6M shares
Diluted Shares Outstanding

Balance Sheet

Concept	2017	2016 Q4	2016 Q3
SHORT-TERM ASSETS
Cash & Short-Term Investments	$681.0M	$546.0M	$532.0M
YoY Change	24.73%	13.75%	43.78%
Cash & Equivalents	$681.0M	$545.5M	$531.8M
Short-Term Investments
Other Short-Term Assets	$1.799B	$633.7M	$601.1M
YoY Change	22.38%	7.92%	-14.13%
Inventory
Prepaid Expenses		$78.40M	$77.90M
Receivables
Other Receivables
Total Short-Term Assets	$7.269B	$4.416B	$4.214B
YoY Change	64.61%	4.8%	4.82%
LONG-TERM ASSETS
Property, Plant & Equipment	$412.0M	$377.6M	$213.9M
YoY Change	8.99%	51.65%	6.58%
Goodwill		$3.753B	$3.763B
YoY Change		2.47%	5.11%
Intangibles		$1.627B	$1.630B
YoY Change		-4.21%	-6.42%
Long-Term Investments
YoY Change
Other Assets	$1.419B	$504.3M	$630.4M
YoY Change	9.07%	13.94%	31.22%
Total Long-Term Assets	$7.641B	$9.112B	$6.987B
YoY Change	8.02%	36.0%	7.65%
TOTAL ASSETS
Total Short-Term Assets	$7.269B	$4.416B	$4.214B
Total Long-Term Assets	$7.641B	$9.112B	$6.987B
Total Assets	$14.91B	$13.53B	$11.20B
YoY Change	29.77%	23.95%	6.56%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable	$4.986B	$2.996B	$2.867B
YoY Change	66.42%	4.14%	5.91%
Accrued Expenses	$948.0M	$772.0M	$651.0M
YoY Change	22.8%	-5.04%	0.46%
Deferred Revenue
YoY Change
Short-Term Debt	$151.0M	$578.0M	$608.0M
YoY Change	19.84%	135.92%	297.39%
Long-Term Debt Due	$290.0M	$578.0M	$608.0M
YoY Change	-49.83%	135.92%	297.39%
Total Short-Term Liabilities	$6.730B	$4.612B	$4.399B
YoY Change	45.92%	10.14%	17.96%
LONG-TERM LIABILITIES
Long-Term Debt	$2.692B	$2.145B	$2.045B
YoY Change	25.5%	3.52%	-3.78%
Other Long-Term Liabilities	$1.188B	$1.078B	$1.016B
YoY Change	10.2%	11.83%	7.1%
Total Long-Term Liabilities	$3.880B	$3.222B	$3.060B
YoY Change	20.38%	6.16%	-0.43%
TOTAL LIABILITIES
Total Short-Term Liabilities	$6.730B	$4.612B	$4.399B
Total Long-Term Liabilities	$3.880B	$3.222B	$3.060B
Total Liabilities	$10.67B	$7.834B	$7.459B
YoY Change	35.23%	8.47%	9.65%
SHAREHOLDERS EQUITY
Retained Earnings		$916.4M	$889.8M
YoY Change		18.32%	14.31%
Common Stock		$3.444B	$3.417B
YoY Change		1.7%	1.39%
Preferred Stock
YoY Change
Treasury Stock (at cost)
YoY Change
Treasury Stock Shares
Shareholders Equity	$4.236B	$3.597B	$3.687B
YoY Change
Total Liabilities & Shareholders Equity	$14.91B	$11.49B	$11.20B
YoY Change	29.77%	5.31%	6.56%

Cashflow Statement

Concept	2017	2016 Q4	2016 Q3
OPERATING ACTIVITIES
Net Income	$481.3M	$95.10M	$122.8M
YoY Change	21.3%	52.65%	-7.88%
Depreciation, Depletion And Amortization	$121.1M	$89.30M	$25.70M
YoY Change	16.89%	-4.8%	7.98%
Cash From Operating Activities	$854.2M	$280.7M	$239.5M
YoY Change	31.5%	-21.94%	0.63%
INVESTING ACTIVITIES
Capital Expenditures	-$129.2M	-$79.00M	-$35.70M
YoY Change	-159.32%	190.44%	35.74%
Acquisitions
YoY Change
Other Investing Activities	-$381.8M	-$105.5M	-$55.80M
YoY Change	42.73%	29.45%	-52.87%
Cash From Investing Activities	-$511.0M	-$184.5M	-$91.50M
YoY Change	5.3%	69.73%	-36.77%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net	-$42.70M
YoY Change	-177.08%
Debt Paid & Issued, Net	$300.0M
YoY Change	500.0%
Cash From Financing Activities	-47.80M	-1.500M	-25.50M
YoY Change	312.07%	-95.44%	-28.37%
NET CHANGE
Cash From Operating Activities	854.2M	280.7M	239.5M
Cash From Investing Activities	-511.0M	-184.5M	-91.50M
Cash From Financing Activities	-47.80M	-1.500M	-25.50M
Net Change In Cash	367.4M	94.70M	122.5M
YoY Change	714.63%	-56.56%	112.31%
FREE CASH FLOW
Cash From Operating Activities	$854.2M	$280.7M	$239.5M
Capital Expenditures	-$129.2M	-$79.00M	-$35.70M
Free Cash Flow	$983.4M	$359.7M	$275.2M
YoY Change	127.74%	-7.01%	4.12%

Facts In Submission

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CY2017Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Liabilities BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities	19600000
CY2017Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Property Plant And Equipment BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment	4600000
CY2017Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssets	602500000
CY2017Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Liabilities Other BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesOther	0
CY2017Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Noncurrent Assets BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentAssets	200000
CY2017Q4	us-gaap	Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Net BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet	545900000
CY2017Q4	us-gaap	Capitalized Computer Software Gross CapitalizedComputerSoftwareGross	291900000
CY2017Q4	us-gaap	Cash And Cash Equivalents At Carrying Value CashAndCashEquivalentsAtCarryingValue	681200000
CY2017Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	2305000000
CY2017Q4	us-gaap	Common Stock Shares Authorized CommonStockSharesAuthorized	400000000	shares
CY2017Q4	us-gaap	Common Stock Shares Outstanding CommonStockSharesOutstanding	181000000	shares
CY2017Q4	us-gaap	Common Stock Shares Issued CommonStockSharesIssued	181000000	shares
CY2017Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	332000000
CY2017Q4	us-gaap	Deferred Tax Liabilities Undistributed Foreign Earnings DeferredTaxLiabilitiesUndistributedForeignEarnings	330000000
CY2017Q4	us-gaap	Common Stock Value CommonStockValue	181000000
CY2017Q4	us-gaap	Construction In Progress Gross ConstructionInProgressGross	20100000
CY2017Q4	us-gaap	Deferred Tax Assets Goodwill And Intangible Assets DeferredTaxAssetsGoodwillAndIntangibleAssets	45800000
CY2017Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	984200000
CY2017Q4	us-gaap	Deferred Tax Assets Net DeferredTaxAssetsNet	905100000
CY2017Q4	us-gaap	Deferred Tax Assets Capital Loss Carryforwards DeferredTaxAssetsCapitalLossCarryforwards	12900000
CY2017Q4	us-gaap	Deferred Tax Assets Liabilities Net DeferredTaxAssetsLiabilitiesNet	573100000
CY2017Q4	us-gaap	Deferred Tax Assets Net Noncurrent DeferredTaxAssetsNetNoncurrent	905100000
CY2017Q4	us-gaap	Deferred Tax Assets Operating Loss Carryforwards DeferredTaxAssetsOperatingLossCarryforwards	30500000
CY2017Q4	us-gaap	Defined Benefit Plan Accumulated Other Comprehensive Income Net Gains Losses Before Tax DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesBeforeTax	-63700000
CY2017Q4	us-gaap	Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate	0.0350	pure
CY2017Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Next Twelve Months DefinedBenefitPlanExpectedFutureBenefitPaymentsNextTwelveMonths	13500000
CY2017Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Five DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFive	15400000
CY2017Q4	us-gaap	Defined Benefit Plan Weighted Average Asset Allocations DefinedBenefitPlanWeightedAverageAssetAllocations	1.000	pure
CY2017Q4	us-gaap	Derivative Assets Current DerivativeAssetsCurrent	7700000
CY2017Q4	us-gaap	Defined Benefit Plan Expected Amortization Next Fiscal Year DefinedBenefitPlanExpectedAmortizationNextFiscalYear	5000000
CY2017Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Five Fiscal Years Thereafter DefinedBenefitPlanExpectedFutureBenefitPaymentsFiveFiscalYearsThereafter	81000000
CY2017Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Three DefinedBenefitPlanExpectedFutureBenefitPaymentsYearThree	14300000
CY2017Q4	us-gaap	Defined Benefit Plan Fair Value Of Plan Assets DefinedBenefitPlanFairValueOfPlanAssets	219400000
CY2017Q4	us-gaap	Derivative Assets Noncurrent DerivativeAssetsNoncurrent	2700000
CY2017Q4	us-gaap	Derivative Liabilities Current DerivativeLiabilitiesCurrent	1600000
CY2017Q4	us-gaap	Derivative Liabilities Noncurrent DerivativeLiabilitiesNoncurrent	1300000
CY2017Q4	us-gaap	Derivative Liability Notional Amount DerivativeLiabilityNotionalAmount	2900000
CY2017Q4	us-gaap	Deferred Rent Credit Current DeferredRentCreditCurrent	4800000
CY2017Q4	us-gaap	Deferred Tax Assets Investments DeferredTaxAssetsInvestments	1100000
CY2017Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	5500000
CY2017Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Accrued Liabilities DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsAccruedLiabilities	28900000
CY2017Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	79100000
CY2017Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets	273800000
CY2017Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Four DefinedBenefitPlanExpectedFutureBenefitPaymentsYearFour	15100000
CY2017Q4	us-gaap	Defined Benefit Plan Expected Future Benefit Payments Year Two DefinedBenefitPlanExpectedFutureBenefitPaymentsYearTwo	14300000
CY2017Q4	us-gaap	Derivative Asset Notional Amount DerivativeAssetNotionalAmount	10300000
CY2017Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	13400000
CY2017Q4	us-gaap	Defined Benefit Plan Amounts Recognized In Balance Sheet DefinedBenefitPlanAmountsRecognizedInBalanceSheet	11700000
CY2017Q4	us-gaap	Defined Benefit Plan Benefit Obligation DefinedBenefitPlanBenefitObligation	271400000
CY2017Q4	us-gaap	Defined Benefit Plan Funded Status Of Plan DefinedBenefitPlanFundedStatusOfPlan	-52000000
CY2017Q4	invest	Derivative Notional Amount DerivativeNotionalAmount	218700000
CY2017Q4	us-gaap	Employee Service Share Based Compensation Nonvested Awards Total Compensation Cost Not Yet Recognized EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized	42800000
CY2017Q4	us-gaap	Escrow Deposit EscrowDeposit	34600000
CY2017Q4	us-gaap	Equity Method Investment Ownership Percentage EquityMethodInvestmentOwnershipPercentage	0.50	pure
CY2017Q4	us-gaap	Equity Method Investment Summarized Financial Information Assets EquityMethodInvestmentSummarizedFinancialInformationAssets	79100000
CY2017Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Next Twelve Months FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths	257200000
CY2017Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Four FiniteLivedIntangibleAssetsAmortizationExpenseYearFour	203400000
CY2017Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Five FiniteLivedIntangibleAssetsAmortizationExpenseYearFive	180600000
CY2017Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Three FiniteLivedIntangibleAssetsAmortizationExpenseYearThree	226700000
CY2017Q4	us-gaap	Finite Lived Intangible Assets Amortization Expense Year Two FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo	243300000
CY2017Q4	us-gaap	Finite Lived Intangible Assets Net FiniteLivedIntangibleAssetsNet	1111200000
CY2017Q4	us-gaap	Finite Lived Noncompete Agreements Gross FiniteLivedNoncompeteAgreementsGross	3600000
CY2017Q4	us-gaap	Finite Lived Trade Names Gross FiniteLivedTradeNamesGross	100000
CY2017Q4	us-gaap	Goodwill Goodwill	4197900000
CY2017Q4	us-gaap	Furniture And Fixtures Gross FurnitureAndFixturesGross	112300000
CY2017Q4	us-gaap	Intangible Assets Net Excluding Goodwill IntangibleAssetsNetExcludingGoodwill	1644600000
CY2017Q4	us-gaap	Leasehold Improvements Gross LeaseholdImprovementsGross	124200000
CY2017Q4	us-gaap	Liabilities Liabilities	8732500000
CY2017Q4	us-gaap	Liabilities And Stockholders Equity LiabilitiesAndStockholdersEquity	12897400000
CY2017Q4	us-gaap	Liabilities Current LiabilitiesCurrent	4912300000
CY2017Q4	us-gaap	Long Term Debt LongTermDebt	19700000
CY2017Q4	us-gaap	Long Term Debt Noncurrent LongTermDebtNoncurrent	2691900000
CY2017Q4	us-gaap	Machinery And Equipment Gross MachineryAndEquipmentGross	28600000
CY2017Q4	us-gaap	Minority Interest MinorityInterest	59700000
CY2017Q4	us-gaap	Other Assets Current OtherAssetsCurrent	708400000
CY2017Q4	us-gaap	Other Liabilities Current OtherLiabilitiesCurrent	56400000
CY2017Q4	us-gaap	Other Assets Noncurrent OtherAssetsNoncurrent	567000000
CY2017Q4	us-gaap	Other Liabilities Noncurrent OtherLiabilitiesNoncurrent	1128300000
CY2017Q4	us-gaap	Pension And Other Postretirement Defined Benefit Plans Liabilities Noncurrent PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent	52000000
CY2017Q4	us-gaap	Premiums And Other Receivables Net PremiumsAndOtherReceivablesNet	2157200000
CY2017Q4	us-gaap	Prepaid Expense Current PrepaidExpenseCurrent	91500000
CY2017Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	412200000
CY2017Q4	us-gaap	Property Plant And Equipment Other PropertyPlantAndEquipmentOther	12000000
CY2017Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	880600000
CY2017Q4	us-gaap	Reinsurance Recoverables ReinsuranceRecoverables	59800000
CY2017Q4	us-gaap	Restricted Cash Current RestrictedCashCurrent	1623800000
CY2017Q4	us-gaap	Retained Earnings Accumulated Deficit RetainedEarningsAccumulatedDeficit	1095900000
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber	10600000	shares
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice	44.95
CY2017Q4	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Exercisable Options Weighted Average Exercise Price1 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1	37.81
CY2017Q4	us-gaap	Stockholders Equity StockholdersEquity	4105200000
CY2017Q4	us-gaap	Short Term Borrowings ShortTermBorrowings	290000000
CY2017Q4	ajg	Deferred Tax Liabilities Other Prepaid Items DeferredTaxLiabilitiesOtherPrepaidItems	10300000
CY2017Q4	ajg	Deferred Tax Liabilities Depreciable Fixed Assets DeferredTaxLiabilitiesDepreciableFixedAssets	26500000
CY2017Q4	ajg	Deferred Tax Liabilities Investment Related Partnerships DeferredTaxLiabilitiesInvestmentRelatedPartnerships	17600000
CY2017Q4	ajg	Accrued Supplemental Direct Bill And Other Receivables Current AccruedSupplementalDirectBillAndOtherReceivablesCurrent	154600000
CY2017Q4	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Intrinsic Value1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1	64000000
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice	44.88
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Aggregate Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingAggregateIntrinsicValue	191100000
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Vested And Expected To Vest Outstanding Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber	10400000	shares
CY2017Q4	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Number Of Exercisable Options ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions	2500000	shares
CY2017Q4	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Number Of Outstanding Options ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions	10600000	shares
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Number ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber	2500000	shares
CY2017Q4	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Exercisable Weighted Average Exercise Price ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice	37.81
CY2017Q4	us-gaap	Stockholders Equity Including Portion Attributable To Noncontrolling Interest StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest	4164900000
CY2017Q4	us-gaap	Unrecognized Tax Benefits UnrecognizedTaxBenefits	10900000
CY2017Q4	us-gaap	Unamortized Debt Issuance Expense UnamortizedDebtIssuanceExpense	6100000
CY2017Q4	us-gaap	Unrecognized Tax Benefits Income Tax Penalties And Interest Accrued UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued	2900000
CY2017Q4	us-gaap	Unrecognized Tax Benefits That Would Impact Effective Tax Rate UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate	9000000
CY2017Q4	ajg	Liabilities Recorded On Self Insurance LiabilitiesRecordedOnSelfInsurance	13500000
CY2017Q4	ajg	Deferred Tax Assets Alternative Minimum Tax And Other Credit Carryforwards DeferredTaxAssetsAlternativeMinimumTaxAndOtherCreditCarryforwards	683300000
CY2017Q4	ajg	Refined Coal Production Related Receivables Current RefinedCoalProductionRelatedReceivablesCurrent	156800000
CY2017Q4	ajg	Deferred Tax Assets Accrued Pension Liability DeferredTaxAssetsAccruedPensionLiability	14800000
CY2017Q4	ajg	Expiration Lists ExpirationLists	241400000
CY2017Q4	ajg	Business Acquisition Cost Of Acquired Entity Purchase Price Net BusinessAcquisitionCostOfAcquiredEntityPurchasePriceNet	545900000
CY2017Q4	ajg	Deferred Tax Liabilities Hedging Instruments DeferredTaxLiabilitiesHedgingInstruments	3800000
CY2017Q4	ajg	Semi Annual Payments Of Interest Net SemiAnnualPaymentsOfInterestNet	3133000000
CY2017Q4	ajg	Business Acquisitions Purchase Price Allocation Goodwill Amount BusinessAcquisitionsPurchasePriceAllocationGoodwillAmount	304500000
CY2017Q4	ajg	Unearned Fees UnearnedFees	74800000
CY2017Q4	ajg	Land And Buildings Gross LandAndBuildingsGross	143600000
CY2017Q4	ajg	Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Aggregate Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingAggregateIntrinsicValue	193400000
CY2017Q4	ajg	Equity Method Investment Summarized Financial Information Funding Commitments EquityMethodInvestmentSummarizedFinancialInformationFundingCommitments	400000
CY2017Q4	ajg	Accrued Compensation And Other Accrued Liabilities AccruedCompensationAndOtherAccruedLiabilities	864100000
CY2017Q4	ajg	Deferred Tax Assets Accrued And Unfunded Compensation And Employee Benefits DeferredTaxAssetsAccruedAndUnfundedCompensationAndEmployeeBenefits	143200000
CY2017Q4	ajg	Maximum Potential Earnout Payable MaximumPotentialEarnoutPayable	201000000
CY2017Q4	ajg	Computer Equipment Gross ComputerEquipmentGross	147900000
CY2017Q4	ajg	Semi Annual Payments Of Interest SemiAnnualPaymentsOfInterest	3139100000
CY2017Q4	ajg	Premium Financing Borrowings PremiumFinancingBorrowings	151100000
CY2017Q4	ajg	Number Of Certified Low Income Housing Developments Investment NumberOfCertifiedLowIncomeHousingDevelopmentsInvestment	8	Investment
CY2017Q4	ajg	Number Of Square Feet NumberOfSquareFeet	360000	sqft
CY2017Q4	ajg	Number Of Commercial Clean Coal Production Facilities NumberOfCommercialCleanCoalProductionFacilities	34	pure
CY2017Q4	ajg	Premiums Payable To Underwriting Enterprises PremiumsPayableToUnderwritingEnterprises	3475900000
CY2015	us-gaap	Adjustment For Amortization AdjustmentForAmortization	240300000
CY2015	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	3500000	shares
CY2015	us-gaap	Amount Recognized In Net Periodic Benefit Cost And Other Comprehensive Income Loss Before Tax AmountRecognizedInNetPeriodicBenefitCostAndOtherComprehensiveIncomeLossBeforeTax	-500000
CY2015	us-gaap	Assumed Premiums Earned AssumedPremiumsEarned	5100000
CY2015	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	4400000
CY2015	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	567900000
CY2015	us-gaap	Brokerage Commissions Revenue BrokerageCommissionsRevenue	1432300000
CY2015	us-gaap	Business Combination Separately Recognized Transactions Additional Disclosures Acquisition Cost Expensed BusinessCombinationSeparatelyRecognizedTransactionsAdditionalDisclosuresAcquisitionCostExpensed	16200000
CY2015	us-gaap	Ceded Premiums Earned CededPremiumsEarned	76800000
CY2015	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	25900000
CY2015	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	210500000
CY2015	us-gaap	Ceded Premiums Written CededPremiumsWritten	75900000
CY2015	us-gaap	Common Stock Dividends Per Share Declared CommonStockDividendsPerShareDeclared	1.48
CY2015	us-gaap	Comprehensive Income Net Of Tax ComprehensiveIncomeNetOfTax	101300000
CY2015	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	127200000
CY2015	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	43900000
CY2015	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	22900000
CY2015	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	18900000
CY2015	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-38600000
CY2015	us-gaap	Cost Of Coal Products And Services CostOfCoalProductsAndServices	1351500000
CY2015	us-gaap	Costs And Expenses CostsAndExpenses	5098900000
CY2015	us-gaap	Defined Benefit Plan Amortization Of Gains Losses DefinedBenefitPlanAmortizationOfGainsLosses	-6200000
CY2015	us-gaap	Defined Benefit Plan Contributions By Employer DefinedBenefitPlanContributionsByEmployer	0
CY2015	us-gaap	Defined Benefit Plan Expected Return On Plan Assets DefinedBenefitPlanExpectedReturnOnPlanAssets	15300000
CY2015	us-gaap	Defined Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	0
CY2015	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Expected Long Term Return On Assets DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostExpectedLongTermReturnOnAssets	0.0725	pure
CY2015	us-gaap	Defined Benefit Plan Service Cost DefinedBenefitPlanServiceCost	1100000
CY2015	us-gaap	Depreciation Amortization And Accretion Net DepreciationAmortizationAndAccretionNet	334200000
CY2015	us-gaap	Derivative Instruments Gain Loss Recognized In Other Comprehensive Income Effective Portion Net DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet	-2800000
CY2015	us-gaap	Derivative Net Hedge Ineffectiveness Gain Loss DerivativeNetHedgeIneffectivenessGainLoss	700000
CY2015	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-139400000
CY2015	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	-3300000
CY2015	us-gaap	Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate	0.0400	pure
CY2015	us-gaap	Defined Benefit Plan Interest Cost DefinedBenefitPlanInterestCost	10800000
CY2015	us-gaap	Depreciation Depreciation	93900000
CY2015	us-gaap	Derivative Instruments Gain Loss Reclassified From Accumulated Oci Into Income Effective Portion Net DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet	700000
CY2015	us-gaap	Defined Benefit Plan Net Periodic Benefit Cost DefinedBenefitPlanNetPeriodicBenefitCost	2800000
CY2015	us-gaap	Direct Premiums Earned DirectPremiumsEarned	71700000
CY2015	us-gaap	Direct Premiums Written DirectPremiumsWritten	71500000
CY2015	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	-0.326	pure
CY2015	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	258300000
CY2015	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.06
CY2015	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.350	pure
CY2015	us-gaap	Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance	0.006	pure
CY2015	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.07
CY2015	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.035	pure
CY2015	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	-75000000
CY2015	us-gaap	Effective Income Tax Rate Reconciliation Change In Enacted Tax Rate EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate	-0.014	pure
CY2015	us-gaap	Effective Income Tax Rate Reconciliation Foreign Income Tax Rate Differential EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential	-0.077	pure
CY2015	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.001	pure
CY2015	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.618	pure
CY2015	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	200000
CY2015	us-gaap	Federal Income Tax Expense Benefit Continuing Operations FederalIncomeTaxExpenseBenefitContinuingOperations	-95500000
CY2015	us-gaap	Foreign Income Tax Expense Benefit Continuing Operations ForeignIncomeTaxExpenseBenefitContinuingOperations	-15700000
CY2015	us-gaap	Foreign Currency Transaction Gain Loss Unrealized ForeignCurrencyTransactionGainLossUnrealized	200000
CY2015	us-gaap	Gain Loss On Sale Of Equity Investments GainLossOnSaleOfEquityInvestments	6700000
CY2015	us-gaap	Gain Loss On Investments GainLossOnInvestments	6600000
CY2015	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	345600000
CY2015	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	293500000
CY2015	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	-52100000
CY2015	us-gaap	Income Taxes Paid IncomeTaxesPaid	78300000
CY2015	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	102700000
CY2015	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	161200000
CY2015	us-gaap	Income Tax Reconciliation Change In Deferred Tax Assets Valuation Allowance IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance	1700000
CY2015	us-gaap	Income Tax Reconciliation Foreign Income Tax Rate Differential IncomeTaxReconciliationForeignIncomeTaxRateDifferential	-22600000
CY2015	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	10200000
CY2015	us-gaap	Income Tax Reconciliation Tax Credits IncomeTaxReconciliationTaxCredits	181300000
CY2015	us-gaap	Increase Decrease In Accrued Income Taxes Payable IncreaseDecreaseInAccruedIncomeTaxesPayable	-18500000
CY2015	us-gaap	Increase Decrease In Premiums Receivable IncreaseDecreaseInPremiumsReceivable	209300000
CY2015	us-gaap	Increase Decrease In Reinsurance Payables IncreaseDecreaseInReinsurancePayables	252200000
CY2015	us-gaap	Impairment Of Intangible Assets Finitelived ImpairmentOfIntangibleAssetsFinitelived	11500000
CY2015	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-200000
CY2015	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	34700000
CY2015	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	89500000
CY2015	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	1000000	shares
CY2015	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	293500000
CY2015	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-95600000
CY2015	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	-4200000
CY2015	us-gaap	Interest Expense InterestExpense	103000000
CY2015	us-gaap	Interest Expense Domestic Deposits InterestExpenseDomesticDeposits	107000000
CY2015	us-gaap	Investment Income Net InvestmentIncomeNet	54200000
CY2015	us-gaap	Interest Expense Foreign Deposits InterestExpenseForeignDeposits	107000000
CY2015	us-gaap	Interest Paid InterestPaid	103900000
CY2015	us-gaap	Labor And Related Expense LaborAndRelatedExpense	2428900000
CY2015	us-gaap	Minority Interest Decrease From Distributions To Noncontrolling Interest Holders MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders	36700000
CY2015	us-gaap	Minority Interest Decrease From Redemptions MinorityInterestDecreaseFromRedemptions	15000000
CY2015	us-gaap	Net Cash Provided By Used In Investing Activities Continuing Operations NetCashProvidedByUsedInInvestingActivitiesContinuingOperations	-368900000
CY2015	us-gaap	Net Cash Provided By Used In Operating Activities Continuing Operations NetCashProvidedByUsedInOperatingActivitiesContinuingOperations	686100000
CY2015	us-gaap	Operating Expenses OperatingExpenses	840700000
CY2015	us-gaap	Net Cash Provided By Used In Financing Activities Continuing Operations NetCashProvidedByUsedInFinancingActivitiesContinuingOperations	-31700000
CY2015	us-gaap	Net Income Loss NetIncomeLoss	356800000
CY2015	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	32300000
CY2015	us-gaap	Number Of Businesses Acquired NumberOfBusinessesAcquired	105	Entity
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CY2015	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Adjustment Net Of Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax	-1300000
CY2015	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Net Of Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax	-2100000
CY2015	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodTax	-1400000
CY2015	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	6200000
CY2015	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Adjustment Net Of Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax	-267500000
CY2015	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-2900000
CY2015	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci Pension And Other Postretirement Benefit Plans For Net Gain Loss Net Of Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax	6200000
CY2015	us-gaap	Other Comprehensive Income Foreign Currency Transaction And Translation Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax	-261100000
CY2015	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax	900000
CY2015	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax	700000
CY2015	us-gaap	Other Sales Revenue Net OtherSalesRevenueNet	30500000
CY2015	us-gaap	Operating Leases Rent Expense Net OperatingLeasesRentExpenseNet	121600000
CY2015	us-gaap	Other Comprehensive Income Loss Foreign Currency Transaction And Translation Reclassification Adjustment From Aoci Realized Upon Sale Or Liquidation Before Tax OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationReclassificationAdjustmentFromAOCIRealizedUponSaleOrLiquidationBeforeTax	0
CY2015	us-gaap	Payments For Previous Acquisition PaymentsForPreviousAcquisition	12100000
CY2015	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	257500000
CY2015	us-gaap	Payments For Proceeds From Investments PaymentsForProceedsFromInvestments	29500000
CY2015	us-gaap	Payments For Capital Improvements PaymentsForCapitalImprovements	99000000
CY2015	us-gaap	Payments To Minority Shareholders PaymentsToMinorityShareholders	39900000
CY2015	us-gaap	Premiums Earned Net PremiumsEarnedNet	0
CY2015	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	203300000
CY2015	us-gaap	Premiums Written Net PremiumsWrittenNet	0
CY2015	us-gaap	Profit Loss ProfitLoss	389100000
CY2015	us-gaap	Proceeds From Lines Of Credit ProceedsFromLinesOfCredit	849000000
CY2015	us-gaap	Proceeds From Repayments Of Debt ProceedsFromRepaymentsOfDebt	23900000
CY2015	us-gaap	Repayments Of Lines Of Credit RepaymentsOfLinesOfCredit	794000000
CY2015	us-gaap	Revenues Revenues	5392400000
CY2015	us-gaap	Share Based Compensation ShareBasedCompensation	11200000
CY2015	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P5Y6M0D
CY2015	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P4Y1M27D
CY2015	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	27.59
CY2015	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Dividend Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate	0.030	pure
CY2015	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Risk Free Interest Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate	0.018	pure
CY2015	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1	P1Y11M1D
CY2015	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod	100000	shares
CY2015	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice	27.59
CY2015	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice	46.19
CY2015	us-gaap	State And Local Income Tax Expense Benefit Continuing Operations StateAndLocalIncomeTaxExpenseBenefitContinuingOperations	15600000
CY2015	us-gaap	Stock Issued During Period Value Acquisitions StockIssuedDuringPeriodValueAcquisitions	346200000
CY2015	us-gaap	Stock Issued During Period Value Other StockIssuedDuringPeriodValueOther	149200000
CY2015	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Grants In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod	394975	shares
CY2015	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Expected Volatility Rate ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate	0.282	pure
CY2015	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1	P4Y1M16D
CY2015	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	1900000	shares
CY2015	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	1400000	shares
CY2015	us-gaap	Stock Issued During Period Value Employee Stock Purchase Plan StockIssuedDuringPeriodValueEmployeeStockPurchasePlan	13800000
CY2015	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	40400000
CY2015	us-gaap	Stock Granted During Period Value Sharebased Compensation StockGrantedDuringPeriodValueSharebasedCompensation	11200000
CY2015	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	172200000	shares
CY2015	ajg	Change In Estimated Acquisition Earnout Payables ChangeInEstimatedAcquisitionEarnoutPayables	40600000
CY2015	ajg	Net Proceeds From Sales Of Operations NetProceedsFromSalesOfOperations	9200000
CY2015	ajg	Earnout Payments For Acquisitions EarnoutPaymentsForAcquisitions	21800000
CY2015	ajg	Revenues From Clean Coal Activities RevenuesFromCleanCoalActivities	1310800000
CY2015	ajg	Net Change In Accrued Compensation And Other Accrued Liabilities NetChangeInAccruedCompensationAndOtherAccruedLiabilities	-217800000
CY2015	ajg	Deferred Compensation And Restricted Stock Expenses Benefit DeferredCompensationAndRestrictedStockExpensesBenefit	6200000
CY2015	ajg	Tax Expense From Issuance Of Common Stock TaxExpenseFromIssuanceOfCommonStock	5300000
CY2015	ajg	Share Based Compensation Arrangement By Share Based Payment Award Options Exercised In Period Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodIntrinsicValue	27000000
CY2015	ajg	Tax Impact From Issuance Of Common Stock TaxImpactFromIssuanceOfCommonStock	5300000
CY2015	ajg	Income Tax Reconciliation Other Permanent Differences IncomeTaxReconciliationOtherPermanentDifferences	-4900000
CY2015	ajg	Commissions Commissions	2338700000
CY2015	ajg	Amortization Of Deferred Compensation And Restricted Stock AmortizationOfDeferredCompensationAndRestrictedStock	22700000
CY2015	ajg	Net Change In Fees Receivable Unearned Fees NetChangeInFeesReceivableUnearnedFees	49600000
CY2015	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	3000000
CY2015	ajg	Weighted Average Number Of Common And Common Equivalent Shares Outstanding WeightedAverageNumberOfCommonAndCommonEquivalentSharesOutstanding	173200000	shares
CY2015	ajg	Effective Income Tax Rate Reconciliation Other Permanent Differences EffectiveIncomeTaxRateReconciliationOtherPermanentDifferences	-0.017	pure
CY2015	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	0.010	pure
CY2015	ajg	Supplemental Revenues SupplementalRevenues	125500000
CY2015	ajg	Contingent Revenues ContingentRevenues	93700000
CY2015	ajg	Payments To Acquire Businesses Net Of Cash And Restricted Cash Acquired PaymentsToAcquireBusinessesNetOfCashAndRestrictedCashAcquired	249600000
CY2017	us-gaap	Adjustment For Amortization AdjustmentForAmortization	264700000
CY2017	dei	Amendment Flag AmendmentFlag	false
CY2017	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	1300000	shares
CY2017	us-gaap	Amount Recognized In Net Periodic Benefit Cost And Other Comprehensive Income Loss Before Tax AmountRecognizedInNetPeriodicBenefitCostAndOtherComprehensiveIncomeLossBeforeTax	-1500000
CY2017	us-gaap	Assumed Premiums Earned AssumedPremiumsEarned	4500000
CY2017	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	5000000
CY2017	us-gaap	Business Acquisition Equity Interests Issued Or Issuable Number Of Shares Issued BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued	688000	shares
CY2017	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	567900000
CY2017	us-gaap	Business Acquisition Pro Forma Earnings Per Share Basic BusinessAcquisitionProFormaEarningsPerShareBasic	2.58
CY2017	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	6222800000
CY2017	us-gaap	Business Combination Consideration Transferred Equity Interests Issued And Issuable BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable	37700000
CY2017	us-gaap	Brokerage Commissions Revenue BrokerageCommissionsRevenue	1636800000
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	2.56
CY2017	us-gaap	Ceded Premiums Earned CededPremiumsEarned	64900000
CY2017	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	37000000
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	665900000
CY2017	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	702900000
CY2017	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	16400000
CY2017	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	29100000
CY2017	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	6700000
CY2017	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-14300000
CY2017	us-gaap	Cost Of Coal Products And Services CostOfCoalProductsAndServices	1635900000
CY2017	us-gaap	Costs And Expenses CostsAndExpenses	5781500000
CY2017	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
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	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 Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	0
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	Derivative Instruments Gain Loss Recognized In Other Comprehensive Income Effective Portion Net DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet	15000000
CY2017	us-gaap	Derivative Net Hedge Ineffectiveness Gain Loss DerivativeNetHedgeIneffectivenessGainLoss	-200000
CY2017	us-gaap	Deferred Federal Income Tax Expense Benefit DeferredFederalIncomeTaxExpenseBenefit	-160400000
CY2017	us-gaap	Deferred State And Local Income Tax Expense Benefit DeferredStateAndLocalIncomeTaxExpenseBenefit	1400000
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	Depreciation Depreciation	121100000
CY2017	us-gaap	Derivative Instruments Gain Loss Reclassified From Accumulated Oci Into Income Effective Portion Net DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet	-5200000
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	Derivatives Methods Of Accounting Hedge Effectiveness DerivativesMethodsOfAccountingHedgeEffectiveness	<div> <p style="MARGIN-BOTTOM: 0px; MARGIN-TOP: 6px"><font style="FONT-FAMILY: Times New Roman" size="2"><b>Hedge Accounting</b></font></p> <p style="MARGIN-BOTTOM: 0px; MARGIN-TOP: 6px"><font style="FONT-FAMILY: Times New Roman" size="2">In August 2017, the FASB issued ASU <font style="WHITE-SPACE: nowrap">No. 2017-12,</font> Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. The new guidance amends the hedge accounting model in the current guidance to enable entities to better portray the economics of their risk management activities in the financial statements and enhance the transparency and understandability of hedge results. The new guidance requires revised tabular disclosures that focus on the effect of hedge accounting by income statement line and the disclosure of the cumulative basis adjustments to the hedged assets and liabilities in fair value hedges. Certain additional disclosures are also required for hedge relationships designated under the <font style="WHITE-SPACE: nowrap"><font style="WHITE-SPACE: nowrap">last-of-layer</font></font> method. The current guidance that requires entities to disclose hedge ineffectiveness has been eliminated because this amount will no longer be separately measured. Under the new guidance, entities will apply the amendments to cash flow and net investment hedge relationships that exist on the date of adoption using a modified retrospective approach (i.e., with a cumulative effect adjustment recorded to the opening balance of retained earnings as of the initial application date). The new guidance also provides transition relief to make it easier for entities to apply certain amendments to existing hedges (including fair value hedges) where the hedge documentation needs to be modified. The presentation and disclosure requirements will be applied prospectively. The new guidance is effective for annual periods beginning after December 15, 2018, including interim periods within those periods. Early adoption is permitted in any interim period or annual year before the effective date. If the guidance is early adopted in an interim period, any adjustments would be reflected as of the beginning of the fiscal year that includes that interim period. We are currently assessing the impact that adopting this new guidance will have on our consolidated financial statements.</font></p> </div>
CY2017	us-gaap	Direct Premiums Earned DirectPremiumsEarned	60400000
CY2017	us-gaap	Direct Premiums Written DirectPremiumsWritten	60700000
CY2017	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	-0.320	pure
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Repatriation Of Foreign Earnings EffectiveIncomeTaxRateReconciliationRepatriationOfForeignEarnings	0.097	pure
CY2017	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	283600000
CY2017	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2017	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2017
CY2017	dei	Document Type DocumentType	10-K
CY2017	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.54
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	0.033	pure
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	-0.040	pure
CY2017	dei	Document Period End Date DocumentPeriodEndDate	2017-12-31
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	2.57
CY2017	dei	Entity Registrant Name EntityRegistrantName	GALLAGHER ARTHUR J & CO
CY2017	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2017	dei	Entity Central Index Key EntityCentralIndexKey	0000354190
CY2017	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	Yes
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Change In Enacted Tax Rate EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate	-0.006	pure
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Foreign Income Tax Rate Differential EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential	-0.128	pure
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	-0.001	pure
CY2017	us-gaap	Gain Loss On Sale Of Equity Investments GainLossOnSaleOfEquityInvestments	3400000
CY2017	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	304500000
CY2017	us-gaap	Effective Income Tax Rate Reconciliation Tax Credits EffectiveIncomeTaxRateReconciliationTaxCredits	0.609	pure
CY2017	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2017	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
CY2017	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	-2800000
CY2017	us-gaap	Federal Income Tax Expense Benefit Continuing Operations FederalIncomeTaxExpenseBenefitContinuingOperations	-144000000
CY2017	us-gaap	Foreign Income Tax Expense Benefit Continuing Operations ForeignIncomeTaxExpenseBenefitContinuingOperations	14800000
CY2017	us-gaap	Foreign Currency Transaction Gain Loss Unrealized ForeignCurrencyTransactionGainLossUnrealized	-2800000
CY2017	us-gaap	Gain Loss On Derivative Instruments Net Pretax GainLossOnDerivativeInstrumentsNetPretax	8300000
CY2017	us-gaap	Gain Loss On Investments GainLossOnInvestments	100000
CY2017	us-gaap	Goodwill Purchase Accounting Adjustments GoodwillPurchaseAccountingAdjustments	14700000
CY2017	us-gaap	Goodwill Translation And Purchase Accounting Adjustments GoodwillTranslationAndPurchaseAccountingAdjustments	110900000
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	278600000
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	378100000
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	99500000
CY2017	us-gaap	Income Taxes Paid IncomeTaxesPaid	55800000
CY2017	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	132400000
CY2017	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	-15100000
CY2017	us-gaap	Income Tax Reconciliation Repatriation Of Foreign Earnings IncomeTaxReconciliationRepatriationOfForeignEarnings	36800000
CY2017	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	183400000
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	-48500000
CY2017	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	5300000
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 Premiums Receivable IncreaseDecreaseInPremiumsReceivable	220300000
CY2017	us-gaap	Increase Decrease In Reinsurance Payables IncreaseDecreaseInReinsurancePayables	334300000
CY2017	us-gaap	Impairment Of Intangible Assets Finitelived ImpairmentOfIntangibleAssetsFinitelived	6200000
CY2017	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-500000
CY2017	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	48500000
CY2017	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	11100000
CY2017	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	2000000	shares
CY2017	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	378100000
CY2017	us-gaap	Income Tax Credits And Adjustments IncomeTaxCreditsAndAdjustments	108000000
CY2017	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-121100000
CY2017	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	-2200000
CY2017	us-gaap	Interest Expense InterestExpense	124100000
CY2017	us-gaap	Interest Expense Domestic Deposits InterestExpenseDomesticDeposits	64200000
CY2017	us-gaap	Investment Income Net InvestmentIncomeNet	56300000
CY2017	us-gaap	Interest Expense Foreign Deposits InterestExpenseForeignDeposits	64200000
CY2017	us-gaap	Interest Paid InterestPaid	124800000
CY2017	us-gaap	Labor And Related Expense LaborAndRelatedExpense	2752300000
CY2017	us-gaap	Minority Interest Decrease From Distributions To Noncontrolling Interest Holders MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders	34400000
CY2017	us-gaap	Minority Interest Decrease From Redemptions MinorityInterestDecreaseFromRedemptions	2100000
CY2017	us-gaap	Net Cash Provided By Used In Investing Activities Continuing Operations NetCashProvidedByUsedInInvestingActivitiesContinuingOperations	-511000000
CY2017	us-gaap	Net Cash Provided By Used In Operating Activities Continuing Operations NetCashProvidedByUsedInOperatingActivitiesContinuingOperations	854200000
CY2017	us-gaap	Number Of Reportable Segments NumberOfReportableSegments	3	Segment
CY2017	us-gaap	Operating Expenses OperatingExpenses	852500000
CY2017	us-gaap	Net Cash Provided By Used In Financing Activities Continuing Operations NetCashProvidedByUsedInFinancingActivitiesContinuingOperations	-47800000
CY2017	us-gaap	Net Income Loss NetIncomeLoss	463100000
CY2017	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	36100000
CY2017	us-gaap	Number Of Businesses Acquired NumberOfBusinessesAcquired	108	Entity
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 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	184300000
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	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	Other Comprehensive Income Foreign Currency Transaction And Translation Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax	183400000
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	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	17600000
CY2017	us-gaap	Payments For Capital Improvements PaymentsForCapitalImprovements	129200000
CY2017	us-gaap	Payments To Acquire Businesses Gross PaymentsToAcquireBusinessesGross	372400000
CY2017	us-gaap	Payments To Minority Shareholders PaymentsToMinorityShareholders	35100000
CY2017	us-gaap	Premiums Earned Net PremiumsEarnedNet	0
CY2017	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	60400000
CY2017	us-gaap	Premiums Written Net PremiumsWrittenNet	0
CY2017	us-gaap	Profit Loss ProfitLoss	499200000
CY2017	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	648000000
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	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	300000000
CY2017	us-gaap	Revenues Revenues	6159600000
CY2017	us-gaap	Share Based Compensation ShareBasedCompensation	17300000
CY2017	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P5Y0M0D
CY2017	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Remaining Contractual Term2 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2	P3Y11M8D
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	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	P1Y8M26D
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures In Period ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod	100000	shares
CY2017	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Forfeitures In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice	34.33
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	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Lower Range Limit ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit	23.76
CY2017	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Upper Range Limit ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit	63.60
CY2017	us-gaap	State And Local Income Tax Expense Benefit Continuing Operations StateAndLocalIncomeTaxExpenseBenefitContinuingOperations	8100000
CY2017	us-gaap	Stock Issued During Period Value Acquisitions StockIssuedDuringPeriodValueAcquisitions	60600000
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	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1	P3Y11M1D
CY2017	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	1700000	shares
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	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	41100000
CY2017	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	1600000
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	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	3300000
CY2017	dei	Trading Symbol TradingSymbol	AJG
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	Variable Interest Entity Ownership Percentage VariableInterestEntityOwnershipPercentage	0.50	pure
CY2017	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 amounts of revenues and expenses related to the potential impact of the adoption of and future accounting under ASC 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, 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>
CY2017	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	180100000	shares
CY2017	ajg	Number Of Countries In Which Company Does Business Through Network Of Correspondent Brokers And Consultants NumberOfCountriesInWhichCompanyDoesBusinessThroughNetworkOfCorrespondentBrokersAndConsultants	150	Country
CY2017	ajg	Number Of Countries In Which Company Has Operations NumberOfCountriesInWhichCompanyHasOperations	32	Country
CY2017	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year Four AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFour	200000
CY2017	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year Five AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearFive	200000
CY2017	ajg	Recorded Earn Out Payable RecordedEarnOutPayable	101200000
CY2017	ajg	Change In Estimated Acquisition Earnout Payables ChangeInEstimatedAcquisitionEarnoutPayables	30900000
CY2017	ajg	Net Proceeds From Sales Of Operations NetProceedsFromSalesOfOperations	3200000
CY2017	ajg	Earnout Payments For Acquisitions EarnoutPaymentsForAcquisitions	41700000
CY2017	ajg	Revenues From Clean Coal Activities RevenuesFromCleanCoalActivities	1560500000
CY2017	ajg	Net Change In Accrued Compensation And Other Accrued Liabilities NetChangeInAccruedCompensationAndOtherAccruedLiabilities	-69300000
CY2017	ajg	Deferred Compensation And Restricted Stock Expenses Benefit DeferredCompensationAndRestrictedStockExpensesBenefit	4800000
CY2017	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year Two AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearTwo	200000
CY2017	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year Three AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThree	200000
CY2017	ajg	Share Based Compensation Arrangement By Share Based Payment Award Options Exercised In Period Intrinsic Value ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodIntrinsicValue	32700000
CY2017	ajg	Business Acquisitions Pro Forma Net Income Loss To Controlling Interest BusinessAcquisitionsProFormaNetIncomeLossToControllingInterest	466300000
CY2017	ajg	Allowances For Estimated Policy Cancellations AllowancesForEstimatedPolicyCancellations	7400000
CY2017	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year Thereafter AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearThereafter	17600000
CY2017	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments Within Year One AmountOfCommitmentExpirationOffBalanceSheetCommitmentsWithinYearOne	1300000
CY2017	ajg	Income Tax Reconciliation Other Permanent Differences IncomeTaxReconciliationOtherPermanentDifferences	-10600000
CY2017	ajg	Amount Of Commitment Expiration Off Balance Sheet Commitments AmountOfCommitmentExpirationOffBalanceSheetCommitments	19700000
CY2017	ajg	Business Combination Aggregate Earnout Obligation Maximum BusinessCombinationAggregateEarnoutObligationMaximum	567900000
CY2017	ajg	Commissions Commissions	2627100000
CY2017	ajg	Amortization Of Deferred Compensation And Restricted Stock AmortizationOfDeferredCompensationAndRestrictedStock	33500000
CY2017	ajg	Net Change In Fees Receivable Unearned Fees NetChangeInFeesReceivableUnearnedFees	-400000
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	Lease Abandonment Charges LeaseAbandonmentCharges	13200000
CY2017	ajg	Weighted Average Number Of Common And Common Equivalent Shares Outstanding WeightedAverageNumberOfCommonAndCommonEquivalentSharesOutstanding	182100000	shares
CY2017	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.
CY2017	ajg	Maturity Period Of Short Term Investments MaturityPeriodOfShortTermInvestments	90 days or less
CY2017	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.
CY2017	ajg	Deferred Equity Participation Sub Plan Distributions To Key Executives Age DeferredEquityParticipationSubPlanDistributionsToKeyExecutivesAge	Age 65
CY2017	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.
CY2017	ajg	Operating Lease Commitment Expiration Date OperatingLeaseCommitmentExpirationDate	2018-02-28
CY2017	ajg	Number Of Employees NumberOfEmployees	2000	Employees
CY2017	ajg	Expected Period Of Return On Plan Assets ExpectedPeriodOfReturnOnPlanAssets	P10Y
CY2017	ajg	Weighted Average Period WeightedAveragePeriod	P4Y
CY2017	ajg	Collateralized Delinquency Receivables Period CollateralizedDelinquencyReceivablesPeriod	P7D
CY2017	ajg	Effective Income Tax Rate Reconciliation Other Permanent Differences EffectiveIncomeTaxRateReconciliationOtherPermanentDifferences	-0.028	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 Changes In Unrecognized Tax Benefits Related To Resolution Of Federal And State Audits Expiration Of Various Statutes Of Limitations And Other Items EffectiveIncomeTaxRateReconciliationChangesInUnrecognizedTaxBenefitsRelatedToResolutionOfFederalAndStateAuditsExpirationOfVariousStatutesOfLimitationsAndOtherItems	-0.002	pure
CY2017	ajg	Acquired Property Through Lease Percentage AcquiredPropertyThroughLeasePercentage	0.60	pure
CY2017	ajg	Acquired Property Through Lease Area AcquiredPropertyThroughLeaseArea	306000	sqft
CY2017	ajg	Proceeds From Settlements On Terminated Interest Rate Swaps ProceedsFromSettlementsOnTerminatedInterestRateSwaps	8300000
CY2017	ajg	Description Of Contracts Renewal Period DescriptionOfContractsRenewalPeriod	One year or less
CY2017	ajg	Supplemental Revenues SupplementalRevenues	163700000
CY2017	ajg	Contingent Revenues ContingentRevenues	111800000
CY2017	ajg	Payments To Acquire Businesses Net Of Cash And Restricted Cash Acquired PaymentsToAcquireBusinessesNetOfCashAndRestrictedCashAcquired	376100000
CY2016	us-gaap	Derivative Instruments Gain Loss Recognized In Other Comprehensive Income Effective Portion Net DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet	-11500000
CY2016	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	5900000	shares
CY2016	us-gaap	Amount Recognized In Net Periodic Benefit Cost And Other Comprehensive Income Loss Before Tax AmountRecognizedInNetPeriodicBenefitCostAndOtherComprehensiveIncomeLossBeforeTax	-900000
CY2016	us-gaap	Assumed Premiums Earned AssumedPremiumsEarned	4900000
CY2016	us-gaap	Assumed Premiums Written AssumedPremiumsWritten	5200000
CY2016	us-gaap	Adjustment For Amortization AdjustmentForAmortization	247200000
CY2016	us-gaap	Business Acquisitions Pro Forma Net Income Loss BusinessAcquisitionsProFormaNetIncomeLoss	567900000
CY2016	us-gaap	Business Acquisition Pro Forma Earnings Per Share Basic BusinessAcquisitionProFormaEarningsPerShareBasic	2.33
CY2016	us-gaap	Business Acquisitions Pro Forma Revenue BusinessAcquisitionsProFormaRevenue	5765900000
CY2016	us-gaap	Brokerage Commissions Revenue BrokerageCommissionsRevenue	1492800000
CY2016	us-gaap	Business Combination Separately Recognized Transactions Additional Disclosures Acquisition Cost Expensed BusinessCombinationSeparatelyRecognizedTransactionsAdditionalDisclosuresAcquisitionCostExpensed	16900000
CY2016	us-gaap	Business Acquisition Pro Forma Earnings Per Share Diluted BusinessAcquisitionProFormaEarningsPerShareDiluted	2.31
CY2016	us-gaap	Ceded Premiums Earned CededPremiumsEarned	74500000
CY2016	us-gaap	Comprehensive Income Net Of Tax Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest	35100000
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	168800000
CY2016	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	203900000
CY2016	us-gaap	Current Federal Tax Expense Benefit CurrentFederalTaxExpenseBenefit	45900000
CY2016	us-gaap	Current Foreign Tax Expense Benefit CurrentForeignTaxExpenseBenefit	22400000
CY2016	us-gaap	Current State And Local Tax Expense Benefit CurrentStateAndLocalTaxExpenseBenefit	8400000
CY2016	us-gaap	Deferred Foreign Income Tax Expense Benefit DeferredForeignIncomeTaxExpenseBenefit	-17800000
CY2016	us-gaap	Cost Of Coal Products And Services CostOfCoalProductsAndServices	1408600000
CY2016	us-gaap	Costs And Expenses CostsAndExpenses	5237900000
CY2016	us-gaap	Defined Benefit Plan Actual Return On Plan Assets DefinedBenefitPlanActualReturnOnPlanAssets	14900000
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 Contribution Plan Employer Discretionary Contribution Amount DefinedContributionPlanEmployerDiscretionaryContributionAmount	0
CY2016	us-gaap	Defined Benefit Plan Actuarial Gain Loss DefinedBenefitPlanActuarialGainLoss	-1800000
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	Depreciation Amortization And Accretion Net DepreciationAmortizationAndAccretionNet	350800000
CY2016	us-gaap	Derivative Net Hedge Ineffectiveness Gain Loss DerivativeNetHedgeIneffectivenessGainLoss	1600000
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	Depreciation Depreciation	103600000
CY2016	us-gaap	Derivative Instruments Gain Loss Reclassified From Accumulated Oci Into Income Effective Portion Net DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet	-8200000
CY2016	us-gaap	Defined Benefit Plan Benefit Obligation Benefits Paid DefinedBenefitPlanBenefitObligationBenefitsPaid	14600000
CY2016	us-gaap	Defined Benefit Plan Net Periodic Benefit Cost DefinedBenefitPlanNetPeriodicBenefitCost	3000000
CY2016	us-gaap	Direct Premiums Earned DirectPremiumsEarned	69600000
CY2016	us-gaap	Direct Premiums Written DirectPremiumsWritten	71800000
CY2016	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	-0.247	pure
CY2016	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	272500000
CY2016	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.32
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	0.039	pure
CY2016	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.33
CY2016	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.015	pure
CY2016	us-gaap	Effect Of Exchange Rate On Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	-107600000
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	-0.096	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	0.545	pure
CY2016	us-gaap	Foreign Currency Transaction Gain Loss Before Tax ForeignCurrencyTransactionGainLossBeforeTax	3000000
CY2016	us-gaap	Federal Income Tax Expense Benefit Continuing Operations FederalIncomeTaxExpenseBenefitContinuingOperations	-100800000
CY2016	us-gaap	Foreign Income Tax Expense Benefit Continuing Operations ForeignIncomeTaxExpenseBenefitContinuingOperations	4600000
CY2016	us-gaap	Foreign Currency Transaction Gain Loss Unrealized ForeignCurrencyTransactionGainLossUnrealized	3000000
CY2016	us-gaap	Gain Loss On Sale Of Equity Investments GainLossOnSaleOfEquityInvestments	6600000
CY2016	us-gaap	Goodwill Acquired During Period GoodwillAcquiredDuringPeriod	225400000
CY2016	us-gaap	Gain Loss On Investments GainLossOnInvestments	6500000
CY2016	us-gaap	Goodwill Purchase Accounting Adjustments GoodwillPurchaseAccountingAdjustments	3400000
CY2016	us-gaap	Goodwill Translation And Purchase Accounting Adjustments GoodwillTranslationAndPurchaseAccountingAdjustments	-123900000
CY2016	us-gaap	Income Loss From Continuing Operations Before Income Taxes Domestic IncomeLossFromContinuingOperationsBeforeIncomeTaxesDomestic	351300000
CY2016	us-gaap	Income Loss From Continuing Operations Before Income Taxes Extraordinary Items Noncontrolling Interest IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest	356900000
CY2016	us-gaap	Income Loss From Continuing Operations Before Income Taxes Foreign IncomeLossFromContinuingOperationsBeforeIncomeTaxesForeign	5600000
CY2016	us-gaap	Income Taxes Paid IncomeTaxesPaid	66100000
CY2016	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	124900000
CY2016	us-gaap	Increase Decrease In Deferred Income Taxes IncreaseDecreaseInDeferredIncomeTaxes	158000000
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	-34100000
CY2016	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	5300000
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 Premiums Receivable IncreaseDecreaseInPremiumsReceivable	242800000
CY2016	us-gaap	Increase Decrease In Reinsurance Payables IncreaseDecreaseInReinsurancePayables	240200000
CY2016	us-gaap	Impairment Of Intangible Assets Finitelived ImpairmentOfIntangibleAssetsFinitelived	1800000
CY2016	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	300000
CY2016	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	55200000
CY2016	us-gaap	Increase Decrease In Other Operating Capital Net IncreaseDecreaseInOtherOperatingCapitalNet	34500000
CY2016	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	800000	shares
CY2016	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	356900000
CY2016	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	-88100000
CY2016	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	-1500000
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CY2016	us-gaap	Minority Interest Decrease From Distributions To Noncontrolling Interest Holders MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders	34100000
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CY2016	us-gaap	Net Income Loss Attributable To Noncontrolling Interest NetIncomeLossAttributableToNoncontrollingInterest	30600000
CY2016	us-gaap	Number Of Businesses Acquired NumberOfBusinessesAcquired	101	Entity
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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	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	Other Comprehensive Income Foreign Currency Transaction And Translation Gain Loss Arising During Period Net Of Tax OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationGainLossArisingDuringPeriodNetOfTax	-231800000
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	Other Sales Revenue Net OtherSalesRevenueNet	-1300000
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	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	Premiums Earned Net PremiumsEarnedNet	0
CY2016	us-gaap	Proceeds From Issuance Of Common Stock ProceedsFromIssuanceOfCommonStock	45600000
CY2016	us-gaap	Premiums Written Net PremiumsWrittenNet	0
CY2016	us-gaap	Profit Loss ProfitLoss	445000000
CY2016	us-gaap	Proceeds From Issuance Of Long Term Debt ProceedsFromIssuanceOfLongTermDebt	376000000
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	Repayments Of Long Term Debt RepaymentsOfLongTermDebt	50000000
CY2016	us-gaap	Revenues Revenues	5594800000
CY2016	us-gaap	Share Based Compensation ShareBasedCompensation	14700000
CY2016	us-gaap	Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Expected Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1	P5Y6M0D
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CY2016	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Exercises In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice	29.50
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	Sharebased Compensation Arrangement By Sharebased Payment Award Options Exercisable Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1	P1Y8M23D
CY2016	us-gaap	Share Based Compensation Arrangements By Share Based Payment Award Options Grants In Period Weighted Average Exercise Price ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice	43.72
CY2016	us-gaap	State And Local Income Tax Expense Benefit Continuing Operations StateAndLocalIncomeTaxExpenseBenefitContinuingOperations	8100000
CY2016	us-gaap	Stock Issued During Period Value Acquisitions StockIssuedDuringPeriodValueAcquisitions	91600000
CY2016	us-gaap	Stock Issued During Period Value Other StockIssuedDuringPeriodValueOther	-101000000
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	Sharebased Compensation Arrangement By Sharebased Payment Award Options Vested And Expected To Vest Outstanding Weighted Average Remaining Contractual Term1 SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1	P4Y1M13D
CY2016	us-gaap	Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Gross ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross	2600000	shares
CY2016	us-gaap	Stock Issued During Period Shares Acquisitions StockIssuedDuringPeriodSharesAcquisitions	91600000	shares
CY2016	us-gaap	Stock Issued During Period Shares Stock Options Exercised StockIssuedDuringPeriodSharesStockOptionsExercised	1100000	shares
CY2016	us-gaap	Stock Issued During Period Value Employee Stock Purchase Plan StockIssuedDuringPeriodValueEmployeeStockPurchasePlan	15900000
CY2016	us-gaap	Stock Issued During Period Value Stock Options Exercised StockIssuedDuringPeriodValueStockOptionsExercised	29700000
CY2016	us-gaap	Unrecognized Tax Benefits Increases Resulting From Current Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions	2400000
CY2016	us-gaap	Stock Granted During Period Value Sharebased Compensation StockGrantedDuringPeriodValueSharebasedCompensation	14700000
CY2016	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions	2200000
CY2016	us-gaap	Unrecognized Tax Benefits Decreases Resulting From Settlements With Taxing Authorities UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities	1400000
CY2016	us-gaap	Unrecognized Tax Benefits Increases Resulting From Prior Period Tax Positions UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions	1800000
CY2016	us-gaap	Unrecognized Tax Benefits Reductions Resulting From Lapse Of Applicable Statute Of Limitations UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations	1800000
CY2016	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	177600000	shares
CY2016	ajg	Change In Estimated Acquisition Earnout Payables ChangeInEstimatedAcquisitionEarnoutPayables	32100000
CY2016	ajg	Net Proceeds From Sales Of Operations NetProceedsFromSalesOfOperations	7800000
CY2016	ajg	Earnout Payments For Acquisitions EarnoutPaymentsForAcquisitions	45500000
CY2016	ajg	Revenues From Clean Coal Activities RevenuesFromCleanCoalActivities	1350100000
CY2016	ajg	Net Change In Accrued Compensation And Other Accrued Liabilities NetChangeInAccruedCompensationAndOtherAccruedLiabilities	-69100000
CY2016	ajg	Deferred Compensation And Restricted Stock Expenses Benefit DeferredCompensationAndRestrictedStockExpensesBenefit	100000
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	Business Acquisitions Pro Forma Net Income Loss To Controlling Interest BusinessAcquisitionsProFormaNetIncomeLossToControllingInterest	414500000
CY2016	ajg	Allowances For Estimated Policy Cancellations AllowancesForEstimatedPolicyCancellations	7100000
CY2016	ajg	Tax Impact From Issuance Of Common Stock TaxImpactFromIssuanceOfCommonStock	6500000
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CY2016	ajg	Amortization Of Deferred Compensation And Restricted Stock AmortizationOfDeferredCompensationAndRestrictedStock	28500000
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CY2016	ajg	Effective Income Tax Rate Reconciliation Other Permanent Differences EffectiveIncomeTaxRateReconciliationOtherPermanentDifferences	-0.013	pure
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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	0.006	pure
CY2016	ajg	Supplemental Revenues SupplementalRevenues	147000000
CY2016	ajg	Contingent Revenues ContingentRevenues	107200000
CY2016	ajg	Payments To Acquire Businesses Net Of Cash And Restricted Cash Acquired PaymentsToAcquireBusinessesNetOfCashAndRestrictedCashAcquired	243400000
	us-gaap	Number Of Businesses Acquired NumberOfBusinessesAcquired	459	Entity
CY2017Q1	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1360400000
CY2017Q1	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.31
CY2017Q1	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	52300000
CY2017Q1	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.31
CY2017Q1	us-gaap	Net Income Loss NetIncomeLoss	55700000
CY2017Q1	us-gaap	Revenues Revenues	1412700000
CY2016Q1	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1244700000
CY2016Q1	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.26
CY2016Q1	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	55700000
CY2016Q1	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.26
CY2016Q1	us-gaap	Net Income Loss NetIncomeLoss	46500000
CY2016Q1	us-gaap	Revenues Revenues	1300400000
CY2016Q2	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1289600000
CY2016Q2	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.85
CY2016Q2	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	137500000
CY2016Q2	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.84
CY2016Q2	us-gaap	Net Income Loss NetIncomeLoss	150000000
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CY2017Q2	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1416400000
CY2017Q2	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.96
CY2017Q2	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	147000000
CY2017Q2	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.95
CY2017Q2	us-gaap	Net Income Loss NetIncomeLoss	171900000
CY2017Q2	us-gaap	Revenues Revenues	1563400000
CY2016Q3	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1387400000
CY2016Q3	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.69
CY2016Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	94900000
CY2016Q3	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.69
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CY2016Q3	us-gaap	Revenues Revenues	1482300000
CY2017Q3	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1487800000
CY2017Q3	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.72
CY2017Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	96700000
CY2017Q3	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.71
CY2017Q3	us-gaap	Net Income Loss NetIncomeLoss	130400000
CY2017Q3	us-gaap	Revenues Revenues	1584500000
CY2016Q4	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1316200000
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CY2016Q4	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	68800000
CY2016Q4	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.53
CY2016Q4	us-gaap	Net Income Loss NetIncomeLoss	95100000
CY2016Q4	us-gaap	Revenues Revenues	1385000000
CY2017Q4	us-gaap	Benefits Losses And Expenses BenefitsLossesAndExpenses	1516900000
CY2017Q4	us-gaap	Income Loss From Continuing Operations Per Basic Share IncomeLossFromContinuingOperationsPerBasicShare	0.58
CY2017Q4	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	82100000
CY2017Q4	us-gaap	Income Loss From Continuing Operations Per Diluted Share IncomeLossFromContinuingOperationsPerDilutedShare	0.57
CY2017Q4	us-gaap	Net Income Loss NetIncomeLoss	105100000
CY2017Q4	us-gaap	Revenues Revenues	1599000000

Files In Submission

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2017 Form 10-K Financial Statement

#000119312518038261 Filed on February 12, 2018

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

2017 Form 10-K Financial Statement

#000119312518038261 Filed on February 12, 2018

Income Statement

Balance Sheet

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Facts In Submission

Files In Submission

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Arthur J. Gallagher & Co. Stock $ajg