XML 69 R56.htm IDEA: XBRL DOCUMENT
v3.21.2

Debt - Senior Notes and Junior Subordinated Notes (Details) | 9 Months Ended
--- | ---
Sep. 30, 2021
2024 Senior Notes | Senior notes |
Debt Instrument [Line Items] |
Redemption price percentage | 100.00%
2024 Senior Notes | Senior notes | Treasury Rate |
Debt Instrument [Line Items] |
Applicable basis spread over redemption price percentage | 0.25%
2025 Senior Notes | Senior notes |
Debt Instrument [Line Items] |
Redemption price percentage | 100.00%
2025 Senior Notes | Senior notes | Treasury Rate |
Debt Instrument [Line Items] |
Applicable basis spread over redemption price percentage | 0.25%
2030 Senior Notes | Senior notes |
Debt Instrument [Line Items] |
Redemption price percentage | 100.00%
2030 Senior Notes | Senior notes | Treasury Rate |
Debt Instrument [Line Items] |
Applicable basis spread over redemption price percentage | 0.40%
5.875% Junior Subordinated Notes due 2059 | Junior subordinated notes | On or after September 30, 2026 |
Debt Instrument [Line Items] |
Redemption price percentage | 100.00%
5.875% Junior Subordinated Notes due 2059 | Junior subordinated notes | If changes in tax laws and interpretations occur |
Debt Instrument [Line Items] |
Redemption price percentage | 100.00%
5.875% Junior Subordinated Notes due 2059 | Junior subordinated notes | If a rating agency makes certain changes relating to the equity credit criteria for securities |
Debt Instrument [Line Items] |
Redemption price percentage | 102.00%
4.750% Junior Subordinated Notes due 2060 | Junior subordinated notes | On or after September 30, 2026 |
Debt Instrument [Line Items] |
Redemption price percentage | 100.00%
4.750% Junior Subordinated Notes due 2060 | Junior subordinated notes | If changes in tax laws and interpretations occur |
Debt Instrument [Line Items] |
Redemption price percentage | 100.00%
4.750% Junior Subordinated Notes due 2060 | Junior subordinated notes | If a rating agency makes certain changes relating to the equity credit criteria for securities |
Debt Instrument [Line Items] |
Redemption price percentage | 102.00%
4.200% Junior Subordinated Notes due 2061 | Junior subordinated notes | On or after September 30, 2026 |
Debt Instrument [Line Items] |
Redemption price percentage | 100.00%
4.200% Junior Subordinated Notes due 2061 | Junior subordinated notes | If changes in tax laws and interpretations occur |
Debt Instrument [Line Items] |
Redemption price percentage | 100.00%
4.200% Junior Subordinated Notes due 2061 | Junior subordinated notes | If a rating agency makes certain changes relating to the equity credit criteria for securities |
Debt Instrument [Line Items] |
Redemption price percentage | 102.00%

X
- Definition Debt Instrument, Make Whole Premium, Discount Rate, Basis Spread on Variable Rate + References No definition available. + Details
Name: | amg_DebtInstrumentMakeWholePremiumDiscountRateBasisSpreadonVariableRate
Namespace Prefix: | amg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

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 Percentage price of original principal amount of debt at which debt can be redeemed by the issuer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph e -URI http://asc.fasb.org/extlink&oid=123599511&loc=d3e64711-112823 + Details
Name: | us-gaap_DebtInstrumentRedemptionPricePercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DebtInstrumentAxis=amg_SeniorNotesFourPointTwoFivePercentDue2024Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_VariableRateAxis=amg_TreasuryRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=amg_SeniorNotesThreePointFiveZeroPercentDue2025Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=amg_SeniorNotesThreePointThreeZeroPercentDue2030Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=amg_FivePointEightSeventyFiveJuniorSubordinatedNotesDue2059Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

X
- Details
Name: | us-gaap_DebtInstrumentRedemptionPeriodAxis=us-gaap_DebtInstrumentRedemptionPeriodOneMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentRedemptionPeriodAxis=us-gaap_DebtInstrumentRedemptionPeriodTwoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentRedemptionPeriodAxis=us-gaap_DebtInstrumentRedemptionPeriodThreeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=amg_FourPointSevenFivePercentJuniorSubordinatedNotesDue2060Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=amg_FourPointTwoPercentJuniorSubordinatedNotesDue2061Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |