XML 71 R60.htm IDEA: XBRL DOCUMENT v3.19.1

Credit and Other Debt Agreements - Summary of Corporate and Other Debt (Parenthetical) (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic payments of interest and principal, expiry date	2020	2020
Fixed Rate of 3.20%, Balloon Due June 24, 2019 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.20%	3.20%
Periodic payments of interest and principal, expiry date	2019	2019
Fixed Rate of 5.85%, balloon Due November 30, 2019 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.85%	5.85%
Periodic payments of interest and principal, expiry date	2019	2019
Fixed Rate of 3.48%, Balloon Due June 24, 2020 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.48%	3.48%
Periodic payments of interest and principal, expiry date	2020	2020
Fixed Rate of 3.99%, Balloon Due July 10, 2020 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.99%	3.99%
Periodic payments of interest and principal, expiry date	2020	2020
Fixed Rate of 5.18%, Balloon Due February 10, 2021 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.18%	5.18%
Periodic payments of interest and principal, expiry date	2021	2021
Prime or LIBOR Plus up to 1.45%, Expires April 8, 2021 [Member] | Credit Agreement [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	1.45%	1.45%
Periodic payments of interest and principal, expiry date	2021	2021
Fixed Rate of 3.69%, Balloon Due June 14, 2022 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.69%	3.69%
Periodic payments of interest and principal, expiry date	2022	2022
Fixed Rate of 5.49%, Balloon Due February 10, 2023 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.49%	5.49%
Periodic payments of interest and principal, expiry date	2023	2023
Fixed Rate of 4.13%, Balloon Due June 24, 2023 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.13%	4.13%
Periodic payments of interest and principal, expiry date	2023	2023
Floating Rate of 1.65% LIBOR Plus Balloon Due August 2, 2023 [Member]
Debt Instrument [Line Items]
Quarterly payments of interest rate	1.65%	1.65%
Periodic payments of interest and principal, expiry date	2023	2023
Quarterly payments of interest, description	90 day LIBOR plus	90 day LIBOR plus
Fixed Rate of 4.72%, Balloon due February 13, 2024 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.72%	4.72%
Periodic payments of interest and principal, expiry date	2024	2024
Fixed Rate of 4.58%, Balloon Due February 27, 2024 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.58%	4.58%
Periodic payments of interest and principal, expiry date	2024	2024
Floating Interest Rate of 1.40% LIBOR Plus Balloon Due June 13, 2024 [Member]
Debt Instrument [Line Items]
Quarterly payments of interest rate	1.40%	1.40%
Periodic payments of interest and principal, expiry date	2024	2024
Quarterly payments of interest, description	90 day LIBOR plus	90 day LIBOR plus
Fixed Rate of 4.31%, Balloon Due June 24, 2025 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.31%	4.31%
Periodic payments of interest and principal, expiry date	2025	2025
Fixed Rate of 4.85%, Balloon due February 13, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.85%	4.85%
Periodic payments of interest and principal, expiry date	2026	2026
Fixed Rate of 4.73%, Balloon Due February 27, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.73%	4.73%
Periodic payments of interest and principal, expiry date	2026	2026
Fixed Rate of 4.40%, Balloon Due June 2, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.40%	4.40%
Periodic payments of interest and principal, expiry date	2026	2026
Fixed Rate of 4.36%, Balloon Due June 24, 2026 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.36%	4.36%
Periodic payments of interest and principal, expiry date	2026	2026
Fixed Rate of 4.09%, Balloon Due June 27, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.09%	4.09%
Periodic payments of interest and principal, expiry date	2027	2027
Fixed Rate of 4.09%, Balloon Due August 2, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.09%	4.09%
Periodic payments of interest and principal, expiry date	2027	2027
Fixed Rate of 4.14%, Balloon Due August 4, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.14%	4.14%
Periodic payments of interest and principal, expiry date	2027	2027
Fixed Rate of 3.46%, Balloon Due December 1, 2027 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	3.46%	3.46%
Periodic payments of interest and principal, expiry date	2027	2027
Fixed Rate of 4.55%, Balloon Due June 2, 2028 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.55%	4.55%
Periodic payments of interest and principal, expiry date	2028	2028
Fixed Rate of 4.34%, Balloon due June 13, 2028 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%	4.34%
Periodic payments of interest and principal, expiry date	2028	2028
Fixed Rate of 5.04%, Balloon due February 13, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.04%	5.04%
Periodic payments of interest and principal, expiry date	2029	2029
Fixed Rate of 4.98%, Balloon Due February 27, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.98%	4.98%
Periodic payments of interest and principal, expiry date	2029	2029
Fixed Rate of 4.19%, Balloon Due June 27, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.19%	4.19%
Periodic payments of interest and principal, expiry date	2029	2029
Fixed Rate of 4.19%, Balloon Due August 2, 2029 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.19%	4.19%
Periodic payments of interest and principal, expiry date	2029	2029
Fixed Rate of 4.44% Balloon Due June 13, 2030 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.44%	4.44%
Periodic payments of interest and principal, expiry date	2030	2030
Fixed Rate of 5.14%, Balloon due March 13, 2031 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.14%	5.14%
Periodic payments of interest and principal, expiry date	2031	2031
Fixed Rate of 4.70%, Balloon Due June 2, 2031 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.70%	4.70%
Periodic payments of interest and principal, expiry date	2031	2031
Fixed Rate of 4.34%, Balloon Due June 27, 2032 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%	4.34%
Periodic payments of interest and principal, expiry date	2032	2032
Fixed Rate of 4.34%, Balloon Due August 2, 2032 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.34%	4.34%
Periodic payments of interest and principal, expiry date	2032	2032
Fixed Rate of 4.59% Balloon Due June 13, 2033 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.59%	4.59%
Periodic payments of interest and principal, expiry date	2033	2033
Fixed Rate of 5.29%, balloon due March 13, 2034 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.29%	5.29%
Periodic payments of interest and principal, expiry date	2034	2034
Fixed Rate of 4.69% Balloon Due June 13, 2038 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	4.69%	4.69%
Periodic payments of interest and principal, expiry date	2038	2038
Fixed Rate of 5.45%, balloon due March 13, 2039 [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	5.45%	5.45%
Periodic payments of interest and principal, expiry date	2039	2039
Facility B [Member] | Interbank Rates Plus 1.05% Expires May 18, 2020 [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	1.05%	1.05%
Facility C and D [Member] | Interbank Rates Plus 1.05% Expires May 18, 2020 [Member] | Premium Financing Debt Facility [Member]
Debt Instrument [Line Items]
Periodic Payment of Interest	0.55%	0.55%

X

- Definition

Debt Instrument Maturity Year

+ References

No definition available.

+ Details

Name:	ajg_DebtInstrumentMaturityYear
Namespace Prefix:	ajg_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentDescriptionOfVariableRateBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=ajg_PremiumFinancingDebtFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfThreePointTwoZeroPercentBalloonDueJuneTwentyFourTwoThousandNineteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFivePointEightFivePercentFiftyMillionDollarsDueNovemberThirtyTwoThousandNineteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfThreePointFourEightPercentBalloonDueJuneTwentyFourTwoThousandTwentyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfThreePointNineNinePercentBalloonDueJulyTenTwoThousandTwentyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFivePointOneEightPercentBalloonDueFebruaryTenTwoThousandTwentyOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_PrimeOrLiborPlusUpToOnePointFourFivePercentExpiresAprilEightTwoThousandTwentyOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=ajg_CreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfThreePointSixNinePercentBalloonDueJuneFourteenTwoThousandTwentyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFivePointFourNinePercentBalloonDueFebruaryTenTwoThousandTwentyThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointOneThreePercentageBalloonDueJuneTwentyFourTwoThousandTwentyThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FloatingInterestRateOfOnePointOneSixFivePercentLIBORPlusBalloonDueAugustTwoTwoThousandTwentyThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointSevenTwoPercentBalloonDueFebruaryThirteenTwoThousandTwentyFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointFiveEightPercentBalloonDueFebruaryTwentySevenTwoThousandTwentyFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FloatingInterestRateOfOnePointFourZeroPercentLIBORPlusBalloonDueJuneThirteenTwoThousandTwentyFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointThreeOnePercentBalloonDueJuneTwentyFourTwoThousandTwentyFiveMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedrateoffourpointeightfivepercentageballoonduefebruarythirteentwothousandtwentysixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointSevenThreePercentBalloonDueFebruaryTwentySevenTwoThousandTwentySixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointFourZeroPercentBalloonDueJuneTwoTwoThousandTwentySixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointThreeSixPercentBalloonDueJuneTwentyFourTwoThousandTwentySixMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointZeroNinePercentBalloonDueJuneTwentySevenTwoThousandTwentySevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointZeroNinePercentBalloonDueAugustTwoTwoThousandTwentySevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointOneFourPercentBalloonDueAugustFourTwoThousandTwentySevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfThreePointFourSixPercentageBalloonDueDecemberOneTwoThousandTwentySevenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointFiveFivePercentBalloonDueJuneTwoTwoThousandTwentyEightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointThreeFourPercentBalloonDueJuneThirteenTwoThousandTwentyEightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedrateoffivepointzerofourpercentballoonduefebruarythirteentwothousandtwentynineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointNineEightPercentBalloonDueFebruaryTwentySevenTwoThousandTwentyNineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointOneNinePercentBalloonDueJuneTwentySevenTwoThousandTwentyNineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointOneNinePercentBalloonDueAugustTwoTwoThousandTwentyNineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointFourFourPercentBalloonDueJuneThirteenTwoThousandThirtyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedrateoffivepointonefourpercentballoonduemarchthriteentwothousandthrityonememberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointSevenZeroPercentBalloonDueJuneTwoTwoThousandThirtyOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointThreeFourPercentBalloonDueJuneTwentySevenTwoThousandThirtyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointThreeFourPercentBalloonDueAugustTwoTwoThousandThirtyTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointFiveNinePercentBalloonDueJuneThirteenTwoThousandThirtyThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedrateoffivepointtwoNinepercentballoonduemarchthriteentwothousandthrityFourmemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfFourPointSixNinePercentBalloonDueJuneThirteenTwoThousandThirtyEightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedrateoffivepointfourFivepercentballoonduemarchthriteentwothousandthrityNinememberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ajg_FacilityBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ExtinguishmentOfDebtAxis=ajg_InterbankRatesPlusOnePointZeroFivePercentExpiresMayEighteenTwoThousandTwentyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ajg_FacilityAndFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: