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Commitments and Contingencies - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Commitments and Contingencies
Co-investment commitments in partnership	$ 187.2
Equity Method Investee | Other Liabilities
Commitments and Contingencies
Total contingent payments	59.8
Payments for Achievement of Financial Targets
Commitments and Contingencies
Total contingent payments	237.1
Contingent payments in year one	89.5
Contingent payments year two through six	147.6
Payment contingent on not meeting financial targets (up to)	12.5
Payment contingent on exercise of option to reduce ownership percentage	25.0
Payments for Contingent Financing
Commitments and Contingencies
Total contingent payments	$ 50.0

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- Definition

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

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No definition available.

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- Definition

The amount that the entity agreed to co-invest in certain investment partnerships where the entity serves as the general partner.

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No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Other Commitment, Contingent Consideration, Asset

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No definition available.

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Balance Type:	debit
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- Definition

Other Commitment, Contingent Consideration, Option To Reduce Ownership Interest, Asset

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No definition available.

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- Definition

Other Commitment, to be Paid, Year Two Through Six

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No definition available.

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Namespace Prefix:	amg_
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Balance Type:	credit
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- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

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No definition available.

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Period Type:	instant

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- Definition

Amount of commitment classified as other to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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No definition available.

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- Details

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