Noncontrolling Interest, Decrease From Affiliate Transaction

No definition available.

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

- Definition

Noncontrolling Interest, Decrease from Transfers to Other Liabilities

+ References

No definition available.

+ Details

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

Name:	amg_NoncontrollingInterestIncreaseFromTransfersToNoncontrollingInterestHolders
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
Namespace Prefix:	amg_
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

Name:	amg_RedeemableNoncontrollingInterestEquityChangeInRedemptionValue
Namespace Prefix:	amg_
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
Namespace Prefix:	amg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Term Of Conditional Right to Put Interest

+ References

No definition available.

+ Details

Name:	amg_TermOfConditionalRighttoPutInterest
Namespace Prefix:	amg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- 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_MinorityInterestLineItems
Namespace Prefix:	us-gaap_
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

Name:	us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Redeemable Non-Controlling Interests (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Redeemable Noncontrolling Interest [Roll Forward]
Balance, beginning balance			$ 465.4
Veritable Transaction			(16.8)
Decrease attributable to consolidated Affiliate sponsored investment products			(6.2)
Transfers to Other liabilities			(57.1)
Transfers from Non-controlling interests			0.1
Changes in redemption value	$ (50.3)	$ (56.0)	46.9	$ (142.9)
Balance, ending balance	432.3		$ 432.3
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	$ 13.9		$ 13.9