Noncontrolling Interest, Decrease from Transfers to Other Liabilities

No definition available.

Name:	amg_NoncontrollingInterestDecreasefromTransferstoOtherLiabilities
Namespace Prefix:	amg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Noncontrolling Interest, Increase from Transfers to Noncontrolling Interest Holders

+ References

No definition available.

+ Details

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Namespace Prefix:	amg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Noncontrolling Interest, Increase (decrease) Attributable to Consolidated Partnerships

+ References

No definition available.

+ Details

Name:	amg_NoncontrollingInterestIncreasedecreaseAttributabletoConsolidatedPartnerships
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Increase (decrease) in redeemable non-controlling interests during the period as a result of a change in the redemption value.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

-- None. No documentation exists for this element. --

+ References

No definition available.

+ Details

Name:	amg_RedeemableNoncontrollingInterestRollForward
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Balance Type:	na
Period Type:	duration

- Definition

Term Of Conditional Right to Put Interest

+ References

No definition available.

+ Details

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- 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

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

As of the reporting date, the aggregate carrying amount of all noncontrolling interests which are redeemable by the (parent) entity (1) at a fixed or determinable price on a fixed or determinable date, (2) at the option of the holder of the noncontrolling interest, or (3) upon occurrence of an event that is not solely within the control of the (parent) entity. This item includes noncontrolling interest holder's ownership (or holders' ownership) regardless of the type of equity interest (common, preferred, other) including all potential organizational (legal) forms of the investee entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Subparagraph (12)(c)
-Section S99
-Paragraph 3A
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480244/480-10-S99-3A

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Subparagraph 14
-Paragraph 3A
-Section S99
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480244/480-10-S99-3A

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Subparagraph 15
-Paragraph 3A
-Section S99
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480244/480-10-S99-3A

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 480
-SubTopic 10
-Subparagraph (16)(c)
-Paragraph 3A
-Section S99
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480244/480-10-S99-3A

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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- Details

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- Details

Name:	srt_ConsolidatedEntitiesAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
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Redeemable Non-Controlling Interests (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Redeemable Noncontrolling Interest [Roll Forward]
Balance, beginning balance			$ 465.4
Decrease attributable to consolidated Affiliate sponsored investment products			(4.1)
Transfers to Other liabilities			(57.7)
Transfers from Non-controlling interests			0.1
Changes in redemption value	$ (4.5)	$ (79.9)	97.2	$ (86.9)
Balance, ending balance	500.9		$ 500.9
Minimum
Noncontrolling Interest [Line Items]
Term of conditional right to put interest			5 years
Maximum
Noncontrolling Interest [Line Items]
Term of conditional right to put interest			15 years
Variable Interest Entity, Primary Beneficiary
Redeemable Noncontrolling Interest [Roll Forward]
Balance, beginning balance			$ 20.1
Balance, ending balance	$ 16.0		$ 16.0