XML 61 R48.htm IDEA: XBRL DOCUMENT
v3.21.2

Fair Value Measurements - Changes in Level 3 Liabilities (Details) - Significant Unobservable Inputs (Level 3) - Affiliate equity purchase obligations - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |
Balance, beginning of period | $ 47.9 | $ 73.3 | $ 22.0 | $ 19.8
Net realized and unrealized (gains) losses | 0.0 | (0.2) | 2.2 | (4.1)
Purchases and issuances | 3.3 | 85.8 | 86.3 | 292.8
Settlements and reductions | (3.5) | (89.0) | (62.8) | (238.6)
Balance, end of period | 47.7 | 69.9 | 47.7 | 69.9
Net change in unrealized (gains) losses relating to instruments still held at the reporting date | $ 0.0 | $ 0.0 | $ 0.0 | $ 0.0

X
- Definition Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Purchases And Issuances + References No definition available. + Details
Name: | amg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchasesAndIssuances
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Liability Settlements And Reductions + References No definition available. + Details
Name: | amg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlementsAndReductions
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings and Other Comprehensive Income (Loss) + References No definition available. + Details
Name: | amg_FairValueMeasurementwithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedinEarningsandOtherComprehensiveIncomeLoss
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of unrealized gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3) and still held. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByLiabilityClassAxis=amg_ObligationsToRelatedPartiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |