XML 69 R58.htm IDEA: XBRL DOCUMENT
v3.21.2

Credit and Other Debt Agreements - Additional Information (Detail) - USD ($) $ in Millions |  |  |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | --- | --- | ---
Aug. 13, 2021 | Jul. 29, 2021 | May 20, 2021 | Sep. 30, 2021 | Sep. 30, 2021
Debt Instrument [Line Items] |  |  |  |  |
Loss on extinguishment of debt | $ 16.2 |  |  | $ 16.2 | $ 16.2
Willis Towers Watson PLC [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Agreement termination date |  | Jul. 29, 2021 |  |  |
Unsecured Senior Notes [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Notes issued and sold |  |  | $ 1,500.0 |  |
Weighted average interest rate |  |  | 3.31% |  |
Realized a cash gain (loss) on hedging transaction |  |  | $ (57.8) |  |
Derivative instrument, term |  |  | 10 years |  |
Fixed Rate of 2.50%, Balloon Due May 20, 2031 [Member] | Unsecured Senior Notes [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Notes issued and sold |  |  | $ 650.0 |  |
Periodic Payment of Interest |  |  | 2.50% |  |
Periodic payments of interest and principal, expiry year |  |  | 2031 |  |
Amount payable to redeem the notes, percent of the principal amount following transaction termination event |  |  | 101.00% |  |
Number of days to occur reinsurance transaction termination event for note redemption |  |  | 30 days |  |
Notes redemption date |  | Aug. 13, 2021 |  |  |
Loss on extinguishment of debt | 16.2 |  |  |  |
Redemption premium | 6.5 |  |  |  |
Unamortized discount amount debt issuance and write-off debt acquisition costs | $ 9.7 |  |  |  |
Fixed Rate of 3.50%, Balloon Due May 20, 2051 [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Periodic Payment of Interest |  |  |  | 3.50% | 3.50%
Fixed Rate of 3.50%, Balloon Due May 20, 2051 [Member] | Unsecured Senior Notes [Member] |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Notes issued and sold |  |  | $ 850.0 |  |
Periodic Payment of Interest |  |  | 3.50% |  |
Periodic payments of interest and principal, expiry year |  |  | 2051 |  |

X
- Definition Agreement termination date. + References No definition available. + Details
Name: | ajg_AgreementTerminationDate
Namespace Prefix: | ajg_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount payable to redeem notes percent of principal amount following transaction termination event. + References No definition available. + Details
Name: | ajg_AmountPayableToRedeemNotesPercentOfPrincipalAmountFollowingTransactionTerminationEvent
Namespace Prefix: | ajg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

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 Debt instrument redemption date. + References No definition available. + Details
Name: | ajg_DebtInstrumentRedemptionDate
Namespace Prefix: | ajg_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of days to occur reinsurance transaction termination event for note redemption. + References No definition available. + Details
Name: | ajg_NumberOfDaysToOccurReinsuranceTransactionTerminationEventForNoteRedemption
Namespace Prefix: | ajg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1B -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611 Reference 2: 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=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types: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
- Definition Weighted average interest rate of debt outstanding. + References No definition available. + Details
Name: | us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_DerivativeTermOfContract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5618551-113959 + Details
Name: | us-gaap_GainLossOnDerivativeInstrumentsNetPretax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 50 -Section 40 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=123467658&loc=d3e12355-112629 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 50 -Section 40 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=123467658&loc=d3e12317-112629 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585 + Details
Name: | us-gaap_GainsLossesOnExtinguishmentOfDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Reflects the difference between the fair value of payments made to legally extinguish a debt and its carrying value at that time. This item excludes the write-off of amounts previously capitalized as debt issuance costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 50 -Section 40 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=123467658&loc=d3e12317-112629 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 50 -Section 40 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=123467658&loc=d3e12355-112629 + Details
Name: | us-gaap_GainsLossesOnExtinguishmentOfDebtBeforeWriteOffOfDeferredDebtIssuanceCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The fair value of notes issued in noncash investing and financing activities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=123431023&loc=d3e4313-108586 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=123431023&loc=d3e4332-108586 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=123431023&loc=d3e4304-108586 + Details
Name: | us-gaap_NotesIssued1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The excess of the (1) fair value of consideration transferred to the holders of a security in excess of (2) the carrying amount of the security reported on the registrant's balance sheet, which will be deducted from net earnings to derive net earnings available to common shareholders. This amount is generally an adjustment considered in the computation of earnings per share. + References No definition available. + Details
Name: | us-gaap_RedemptionPremium
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=ajg_WillisTowersWatsonPLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=ajg_SeniorUnsecuredNoteMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfTwoPointFiveZeroPercentBalloonDueMayTwentyTwoThousandThirtyOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ExtinguishmentOfDebtAxis=ajg_FixedRateOfThreePointFiveZeroPercentBalloonDueMayTwentyTwoThousandFiftyOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |