XML 75 R63.htm IDEA: XBRL DOCUMENT
v3.25.3

Equity Method Investments in Affiliates - Change in Equity Method Investments (Details) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Dec. 31, 2024
Change in Equity Method Investments in Affiliates [Roll Forward] |  |  |
Balance, as of December 31, 2024 | $ 2,246.6 |  |
Distributions of earnings | (379.7) | $ (357.3) |
Return of capital | (3.8) | $ 0.0 |
Balance, as of September 30, 2025 | 2,529.1 |  |
Equity Method Investee |  |  |
Change in Equity Method Investments in Affiliates [Roll Forward] |  |  |
Balance, as of December 31, 2024 | 2,246.6 |  |
Investments in Affiliates | 538.0 |  |
Affiliate transactions | (125.6) |  |
Earnings, net of tax | 299.7 |  |
Intangible amortization and impairments | (70.2) |  |
Distributions of earnings | (379.1) |  |
Return of capital | (3.8) |  |
Foreign currency translation | 23.5 |  |
Balance, as of September 30, 2025 | 2,529.1 |  |
Equity method investment, undistributed earnings | $ 123.1 |  | $ 206.1

X
- Definition Change in Equity Method Investments in Affiliates + References No definition available. + Details
Name: | amg_ChangeinEquityMethodInvestmentsinAffiliatesRollForward
Namespace Prefix: | amg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Equity Method Investment, Intangible Asset Amortization and Impairments + References No definition available. + Details
Name: | amg_EquityMethodInvestmentIntangibleAssetAmortizationandImpairments
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Equity Method Investment, Realized Gain (Loss) on Foreign Currency Translation + References No definition available. + Details
Name: | amg_EquityMethodInvestmentRealizedGainLossonForeignCurrencyTranslation
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Equity Method Investment, Undistributed Earnings + References No definition available. + Details
Name: | amg_EquityMethodInvestmentUndistributedEarnings
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Income (Loss) from Equity Method Investments Before Amortization of Intangibles + References No definition available. + Details
Name: | amg_IncomeLossfromEquityMethodInvestmentsBeforeAmortizationofIntangibles
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Obligations And Payments To Acquire Interest In Subsidiaries And Affiliates + References No definition available. + Details
Name: | amg_ObligationsAndPaymentsToAcquireInterestInSubsidiariesAndAffiliates
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Proceeds From Equity Method Investment, Return Of Capital + References No definition available. + Details
Name: | amg_ProceedsFromEquityMethodInvestmentReturnOfCapital
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-28 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(10)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 21D -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482740/230-10-45-21D Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(12)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 + Details
Name: | us-gaap_EquityMethodInvestmentDividendsOrDistributions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of the entity's equity method investment which has been sold. + References No definition available. + Details
Name: | us-gaap_EquityMethodInvestmentSoldCarryingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of investment in equity method investee and investment in and advance to affiliate. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(18)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 + Details
Name: | us-gaap_InvestmentsInAffiliatesSubsidiariesAssociatesAndJointVentures
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_EquityMethodInvesteeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |