XML 113 R98.htm IDEA: XBRL DOCUMENT
v3.20.4

Investments - Other Investments - Additional Information (Detail) | Dec. 31, 2020 USD ($) Venture Investment | Dec. 31, 2019 USD ($)
--- | --- | ---
Schedule of Equity Method Investments [Line Items] |  |
Assets | $ 22,400,000 | $ 40,000,000.0
Non controlling interest certified low-income housing developments | Investment | 8 |
Liabilities | $ 16,098,700,000 | 14,419,300,000
Other Investments [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Assets | 3,900,000 | $ 4,500,000
Other Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Assets | 4,800,000 |
Liabilities | $ 500,000 |
Other Investments [Member] | Four Venture Capital Funds [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Non controlling interest in venture capital funds number | Venture | 4 |
Assets | $ 3,900,000 |
Other Investments [Member] | Eight Certified Low Income Housing Developments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Carrying value of investments | $ 0 |

X
- Definition Carrying Value of Investments + References No definition available. + Details
Name: | ajg_CarryingValueOfInvestments
Namespace Prefix: | ajg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number Of Certified Low Income Housing Developments Investment + References No definition available. + Details
Name: | ajg_NumberOfCertifiedLowIncomeHousingDevelopmentsInvestment
Namespace Prefix: | ajg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Number Of Venture Capital Funds Investment + References No definition available. + Details
Name: | ajg_NumberOfVentureCapitalFundsInvestment
Namespace Prefix: | ajg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 25 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8813-108599 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_EquityMethodInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Sum of the carrying amounts as of the balance sheet date of all liabilities that are recognized. Liabilities are probable future sacrifices of economic benefits arising from present obligations of an entity to transfer assets or provide services to other entities in the future. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=116870748&loc=SL6758485-165988 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=121559654&loc=d3e5710-111685 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19-26) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121559654&loc=d3e5710-111685 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 30 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(g)(1)(ii)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690 + Details
Name: | us-gaap_Liabilities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ajg_VentureCapitalFundsAndOtherMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ConsolidatedEntitiesAxis=us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ajg_Investment1Axis=ajg_FourVentureCapitalFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ajg_Investment1Axis=ajg_EightCertifiedLowIncomeHousingDevelopmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |