XML 71 R60.htm IDEA: XBRL DOCUMENT v3.26.1

Deferred Compensation - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2026	Dec. 31, 2025
Deferred Equity Participation Plan (DEPP)
Investments And Employee Deferred Compensation Plan [Line Items]
Vesting period, years	1 year
Unearned deferred compensation, value	$ 141	$ 81
Unearned deferred compensation, shares (in shares)	1.8	1.8
Total intrinsic value of unvested equity based awards	$ 391	$ 475
Deferred Cash Participation Plan (DCPP)
Investments And Employee Deferred Compensation Plan [Line Items]
Vesting period, years	5 years

X

- Definition

Investments And Employee Deferred Compensation Plan [Line Items]

+ References

No definition available.

+ Details

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

X

- Definition

Unearned Deferred Compensation, Shares

+ References

No definition available.

+ Details

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

X

- Definition

Unearned Deferred Compensation, Value

+ References

No definition available.

+ Details

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

X

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

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

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

+ References

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

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	us-gaap_AwardTypeAxis=ajg_DeferredEquityParticipationPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_AwardTypeAxis=ajg_DeferredCashParticipationPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: