Accounting Standards and Policies (Policies)	3 Months Ended
Accounting Standards and Policies (Policies)	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation	The Consolidated Financial Statements of Affiliated Managers Group, Inc. (“AMG” or the “Company”) have been prepared in accordance with accounting principles generally accepted in the U.S. (“GAAP”) for interim financial information and with the instructions to Form 10-Q and Rule 10-01 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for full year financial statements. In the opinion of management, all normal and recurring adjustments considered necessary for a fair statement of the Company’s interim financial position and results of operations have been included and all intercompany balances and transactions have been eliminated. Operating results for interim periods are not necessarily indicative of the results that may be expected for any other period or for the full year. The Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2023 includes additional information about its operations, financial position, and accounting policies, and should be read in conjunction with this Quarterly Report on Form 10-Q. All amounts in these notes, except per share data in the text and tables herein, are stated in millions unless otherwise indicated
Use of Estimates	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts and disclosures in the financial statements. Actual results could differ from those estimates.
Recently Adopted Accounting Standards and Recent Accounting Developments	Recently Adopted Accounting Standards Effective January 1, 2024, the Company adopted Accounting Standard Update (“ASU”) 2022-03, Fair Value Measurement (Topic 820): Fair Value Measurement of Equity Securities Subject to Contractual Sale Restrictions. The adoption of this standard did not have a material impact on the Company’s Consolidated Financial Statements. Recent Accounting Developments In November 2023, the Financial Accounting Standards Board (“FASB”) issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which requires disclosure of incremental segment information on an annual and interim basis for all public entities to enable investors to develop more decision-useful financial analyses. The standard is effective for annual periods beginning after December 15, 2023 and for interim periods beginning after December 15, 2024. The Company currently does not expect the adoption to have a material impact on its Consolidated Financial Statements. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which requires greater disaggregation of income tax disclosures related to the income tax rate reconciliation and income taxes paid. The standard is effective for annual periods beginning after December 15, 2024. The Company currently does not expect the adoption to have a material impact on its Consolidated Financial Statements. In March 2024, the FASB issued ASU 2024-01, Compensation—Stock Compensation (Topic 718): Scope Application of Profits Interest and Similar Awards, which clarifies how an entity should apply the scope guidance to determine whether profits interest and similar awards should be accounted for in accordance with Topic 718. The standard is effective for interim and annual periods beginning after December 15, 2024 for the Company, and is effective for interim and annual periods beginning after December 15, 2025 for the Company’s Affiliates. The Company is evaluating the impact of this standard, however it currently does not expect the adoption to have a material impact on its Consolidated Financial Statements.
Investments in Affiliates and Affiliate Sponsored Investments Products	Affiliate Sponsored Investment Products The Company’s Affiliates sponsor various investment products where the Affiliate also acts as the investment adviser. These investment products are typically owned primarily by third-party investors; however, certain products are funded with general partner and seed capital investments from the Company and its Affiliates. Third-party investors in Affiliate sponsored investment products are generally entitled to substantially all of the economics of these products, except for the asset- and performance-based fees earned by the Company’s Affiliates or any gains or losses attributable to the Company’s or its Affiliates’ investments in these products. As a result, the Company generally does not consolidate these products. However, for certain products, the Company’s consolidated Affiliates, as the investment manager, have the power to direct the activities of the investment product and have an exposure to the economics of the VIE that is more than insignificant, though generally only for a short period while the product is established and has yet to attract significant third-party investors. When the products are consolidated, the Company retains the specialized investment company accounting principles of the underlying products, and all of the underlying investments are carried at fair value in Investments in marketable securities, with corresponding changes in the investments’ fair values included in Investment and other income. Purchases and sales of securities are included in purchases and sales by consolidated Affiliate sponsored investment products in the Consolidated Statements of Cash Flows, respectively, and the third-party investors’ interests are recorded in Redeemable non-controlling interests. When the Company or its consolidated Affiliates no longer control these products, due to a reduction in ownership or other reasons, the products are deconsolidated with only the Company’s or its consolidated Affiliate’s investment in the product reported from the date of deconsolidation. The Company’s carrying value and maximum exposure to loss from unconsolidated Affiliate sponsored investment products, is its or its consolidated Affiliates’ interests in the unconsolidated net assets of the respective products.