XML 85 R73.htm IDEA: XBRL DOCUMENT v3.25.3

Affiliate Equity - Summary of Affiliate Recognized and Unrecognized Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Affiliate Equity [Line Items]
Affiliate equity compensation expense	$ 43.7	$ 12.1	$ 114.3	$ 46.5
Non- controlling Interests
Affiliate Equity [Line Items]
Non-controlling interests	4.6	9.7	$ 23.1	30.9
Unrecognized Affiliate Equity Expense [Abstract]
Remaining Life			5 years		6 years
Non-controlling Interests	168.2		$ 168.2		$ 206.0
Affiliated Entity
Affiliate Equity [Line Items]
Controlling interest	39.1	$ 2.4	91.2	$ 15.6
Unrecognized Affiliate Equity Expense [Abstract]
Controlling Interest	$ 71.1		$ 71.1		$ 36.7
Remaining Life			3 years		3 years

X

- Definition

Affiliate Equity Compensation Expense, Attributable to Noncontrolling Interest

+ References

No definition available.

+ Details

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

X

- Definition

Affiliate Equity Compensation Expense, Including Portion Attributable to Noncontrolling Interest

+ References

No definition available.

+ Details

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

X

- Definition

[Line Items] for Affiliate Equity [Table]

+ References

No definition available.

+ Details

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

X

- Definition

Affiliate Equity Unrecognized Compensation Expense, Attributable to Noncontrolling Interest

+ References

No definition available.

+ Details

Name:	amg_AffiliateEquityUnrecognizedCompensationExpenseAttributabletoNoncontrollingInterest
Namespace Prefix:	amg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Affiliate Equity, Unrecognized Compensation Expense, Remaining Life

+ References

No definition available.

+ Details

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

X

- Definition

Represents the compensation expenses related to Affiliate equity.

+ References

No definition available.

+ Details

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

X

- Definition

Unrecognized Affiliate Equity Expense [Abstract]

+ References

No definition available.

+ Details

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

X

- Definition

Unrecognized Compensation Expenses Related to Affiliate Equity Attributable to Controlling Interest

+ References

No definition available.

+ Details

Name:	amg_UnrecognizedCompensationExpensesRelatedtoAffiliateEquityAttributabletoControllingInterest
Namespace Prefix:	amg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_NoncontrollingInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=srt_AffiliatedEntityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: