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Equity Distribution Program (Details) - USD ($)	Sep. 30, 2022	Jun. 30, 2022
Equity Distribution Program
Class of Stock [Line Items]
Equity distribution program, maximum amount authorized	$ 0	$ 500,000,000

X

- Definition

Stock Issuable, Value, Maximum

+ References

No definition available.

+ Details

Name:	amg_StockIssuableValueMaximum
Namespace Prefix:	amg_
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_ClassOfStockLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_ForwardContractIndexedToIssuersEquityTypeAxis=amg_ForwardEquityAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: