XML 80 R61.htm IDEA: XBRL DOCUMENT
v3.22.0.1

Other Investments - Schedule of Changes in Other Investments (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020
Other Investments [Roll Forward] |  |
Balance, beginning of period | $ 257.2 | $ 211.8
Net realized and unrealized gains | 116.1 | 23.3
Purchases and commitments | 60.3 | 44.8
Sales and distributions | (58.4) | (22.7)
Balance, end of period | 375.2 | 257.2
Without Readily Determinable Fair Values |  |
Balance, beginning of period | 13.8 | 0.0
Net realized and unrealized gains | 36.6 | 5.3
Purchases and commitments | 0.0 | 8.5
Sales and distributions | 0.0 | 0.0
Balance, end of period | 50.4 | 13.8
Fair Value Measured at NAV |  |
Other Investments [Roll Forward] |  |
Balance, beginning of period | 243.4 | 211.8
Net realized and unrealized gains | 79.5 | 18.0
Purchases and commitments | 60.3 | 36.3
Sales and distributions | (58.4) | (22.7)
Balance, end of period | $ 324.8 | $ 243.4

X
- Definition Equity Securities Without Readily Determinable Fair Value, Net Gain (Loss) + References No definition available. + Details
Name: | amg_EquitySecuritiesWithoutReadilyDeterminableFairValueNetGainLoss
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Equity Securities Without Readily Determinable Fair Value, Purchases And Commitments + References No definition available. + Details
Name: | amg_EquitySecuritiesWithoutReadilyDeterminableFairValuePurchasesAndCommitments
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Equity Securities Without Readily Determinable Fair Value + References No definition available. + Details
Name: | amg_EquitySecuritiesWithoutReadilyDeterminableFairValueRollForward
Namespace Prefix: | amg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Equity Securities Without Readily Determinable Fair Value, Sales And Distributions + References No definition available. + Details
Name: | amg_EquitySecuritiesWithoutReadilyDeterminableFairValueSalesAndDistributions
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Other Investments, Gain (Loss), Net + References No definition available. + Details
Name: | amg_OtherInvestmentsGainLossNet
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Other Investments, Purchases + References No definition available. + Details
Name: | amg_OtherInvestmentsPurchases
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Other Investments + References No definition available. + Details
Name: | amg_OtherInvestmentsRollForward
Namespace Prefix: | amg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Other Investments, Sales + References No definition available. + Details
Name: | amg_OtherInvestmentsSales
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of investment in equity security without readily determinable fair value. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 321 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=123583765&loc=SL75117539-209714 + Details
Name: | us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investments classified as other. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(f,g)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 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 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_OtherInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |