XML 64 R57.htm IDEA: XBRL DOCUMENT v3.25.1

Stock Option Plans - Additional information (Detail) - USD ($) $ / shares in Units, $ in Millions				3 Months Ended
	Mar. 01, 2025	Mar. 01, 2024	May 10, 2022	Mar. 31, 2025	Mar. 31, 2024
Stock Option Plans [Line Items]
Compensation expense related to stock option grants				$ 17.8	$ 15.1
Total intrinsic value of options exercised				162.3	$ 123.4
Total unrecognized compensation cost related to nonvested options				$ 184.4
Weighted average period, years				4 years
Black-Scholes Option Pricing Model [Member]
Stock Option Plans [Line Items]
Weighted average fair value per option for all options				$ 98.27	$ 69.55
Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Stock option granted, Share pool			13,500,000
Shares against the pool			3.8
Maximum number of shares available			3,500,000	2,100,000
Number Of Periods Options Expire				7 years
Shares available for grant				9,900,000
Long Term Incentive Plan [Member] | Officer and Key Employees [Member]
Stock Option Plans [Line Items]
Shares available for grant	829,000	1,044,000
Stock options granted, exercise percentage, on the third anniversary date of the grant	34.00%	34.00%
Stock options granted, exercise percentage, on the fourth anniversary date of the grant	33.00%	33.00%
Stock options granted, exercise percentage, on the fifth anniversary date of the grant	33.00%	33.00%
Long Term Incentive Plan [Member] | Maximum [Member]
Stock Option Plans [Line Items]
Minimum exercise price of stock options, percent of fair market value of a share of common stock on the date of grant				100.00%
Maximum period for the exercise of stock options, years				7 years	7 years
Long Term Incentive Plan [Member] | Minimum [Member] | Executive Officer [Member]
Stock Option Plans [Line Items]
Minimum age of employee with not subject to award forfeiture on condition compliance				62 years

X

- Definition

Age Of Employee No Longer Subject To Award Forfeiture On Condition Compliance

+ References

No definition available.

+ Details

Name:	ajg_AgeOfEmployeeNoLongerSubjectToAwardForfeitureOnConditionCompliance
Namespace Prefix:	ajg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Exercise Price Of Stock Options Percent Of Fair Market Value Of Share Of Common Stock On Date Of Grant.

+ References

No definition available.

+ Details

Name:	ajg_ExercisePriceOfStockOptionsPercentOfFairMarketValueOfShareOfCommonStockOnDateOfGrant
Namespace Prefix:	ajg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Number of years options expire.

+ References

No definition available.

+ Details

Name:	ajg_NumberOfPeriodsOptionsExpire
Namespace Prefix:	ajg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Period for options to expire from date of grant.

+ References

No definition available.

+ Details

Name:	ajg_PeriodForOptionsToExpireFromDateOfGrant
Namespace Prefix:	ajg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Share-based compensation arrangement by share-based payment award, equity instruments other than options, share pool

+ References

No definition available.

+ Details

Name:	ajg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsSharePool
Namespace Prefix:	ajg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Share-based compensation arrangement by share-based payment award, equity instruments other than options, shares against pool

+ References

No definition available.

+ Details

Name:	ajg_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsSharesAgainstPool
Namespace Prefix:	ajg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Share-based compensation arrangement by share based payment award options exercised in period intrinsic value.

+ References

No definition available.

+ Details

Name:	ajg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisedInPeriodIntrinsicValue
Namespace Prefix:	ajg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Share based compensation arrangement by share based payment award options grants in period exercise percentage year one.

+ References

No definition available.

+ Details

Name:	ajg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodExercisePercentageYearOne
Namespace Prefix:	ajg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Share based compensation arrangement by share based payment award options grants in period exercise percentage year three.

+ References

No definition available.

+ Details

Name:	ajg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodExercisePercentageYearThree
Namespace Prefix:	ajg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Share based compensation arrangement by share based payment award options grants in period exercise percentage year two.

+ References

No definition available.

+ Details

Name:	ajg_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodExercisePercentageYearTwo
Namespace Prefix:	ajg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Stock Option Plans [Line Items]

+ References

No definition available.

+ Details

Name:	ajg_StockOptionPlansLineItems
Namespace Prefix:	ajg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Weighted Average Period

+ References

No definition available.

+ Details

Name:	ajg_WeightedAveragePeriod
Namespace Prefix:	ajg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(01)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Value, after forfeiture, of shares granted under share-based payment arrangement. Excludes employee stock ownership plan (ESOP).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 30
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480513/718-10-30-3

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 30
-Section 35
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480843/718-30-35-1

+ Details

Name:	us-gaap_StockGrantedDuringPeriodValueSharebasedCompensation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

Name:	us-gaap_ValuationTechniqueAxis=ajg_BlackScholesOptionPricingModelMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_PlanNameAxis=ajg_LongTermIncentivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_TitleOfIndividualAxis=srt_OfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_TitleOfIndividualAxis=srt_ExecutiveOfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: