Accounting Standards and Policies (Policies)	6 Months Ended
Accounting Standards and Policies (Policies)	Jun. 30, 2023
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. Certain reclassifications have been made to the prior period’s financial statements to conform to the current period’s presentation. 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, 2022 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	Recent Accounting Developments In June 2022, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2022-03, Fair Value Measurement (Topic 820): Fair Value Measurement of Equity Securities Subject to Contractual Sale Restrictions, which clarifies the guidance in Topic 820 on the fair value measurement of an equity security that is subject to a contractual sale restriction and requires specific disclosures related to such an equity security. The standard is effective for interim and annual periods beginning after December 15, 2023 for the Company, and is effective for interim and annual periods beginning after December 15, 2024 for the Company’s Affiliates. The Company is evaluating the impact of this standard and 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	Investments in Affiliates and Affiliate Sponsored Investment Products In evaluating whether an investment must be consolidated, the Company evaluates the risk, rewards, and significant terms of each of its Affiliates and other investments to determine if an investment is considered a voting rights entity (“VRE”) or a variable interest entity (“VIE”). An entity is a VRE when the total equity investment at risk is sufficient to enable the entity to finance its activities independently, and when the equity holders have the obligation to absorb losses, the right to receive residual returns, and the right to direct the activities of the entity that most significantly impact its economic performance. An entity is a VIE when it lacks one or more of the characteristics of a VRE, which, for the Company, are Affiliate investments structured as partnerships (or similar entities) where the Company is a limited partner and lacks substantive kick-out or substantive participation rights over the general partner. Assessing whether an entity is a VRE or VIE involves judgment. Upon the occurrence of certain events, management reviews and reconsiders its previous conclusion regarding the status of an entity as a VRE or a VIE. The Company consolidates VREs when it has control over significant operating, financial, and investing decisions of the entity. When the Company lacks such control, but is deemed to have significant influence, the Company accounts for the VRE under the equity method. Investments with readily determinable fair values in which the Company does not have rights to exercise significant influence are recorded at fair value on the Consolidated Balance Sheets, with changes in fair value included in Investment and other income. The Company consolidates VIEs when it is the primary beneficiary of the entity, which is defined as having the power to direct the activities that most significantly impact the VIE’s economic performance and the obligation to absorb losses of, or the right to receive benefits from, the entity that could potentially be significant to the VIE. Substantially all of the Company’s consolidated Affiliates considered VIEs are controlled because the Company holds a majority of the voting interests or it is the managing member or general partner. Furthermore, an Affiliate’s assets can be used for purposes other than the settlement of the respective Affiliate’s obligations. The Company applies the equity method of accounting to VIEs where the Company is not the primary beneficiary, but has the ability to exercise significant influence over operating and financial matters of the VIE. Investments in Affiliates Substantially all of the Company’s Affiliates are considered VIEs and are either consolidated or accounted for under the equity method. A limited number of the Company’s Affiliates are considered VREs and most of these are accounted for under the equity method. When an Affiliate is consolidated, the portion of the earnings attributable to Affiliate management’s and any co-investor’s equity ownership is included in Net income (non-controlling interests) in the Consolidated Statements of Income. Undistributed earnings attributable to Affiliate management’s and any co-investor’s equity ownership, along with their share of any tangible or intangible net assets, are presented within Non-controlling interests on the Consolidated Balance Sheets. Affiliate equity interests where the holder has certain rights to demand settlement are presented, at their current redemption values, as Redeemable non-controlling interests or Other liabilities on the Consolidated Balance Sheets. The Company periodically issues, sells, and purchases the equity of its consolidated Affiliates. Because these transactions take place between entities that are under common control, any gains or losses attributable to these transactions are required to be included in Additional paid-in capital in the Consolidated Balance Sheets, net of any related income tax effects in the period the transaction occurs. When an Affiliate is accounted for under the equity method, the Company’s share of an Affiliate’s earnings or losses, net of amortization and impairments, is included in Equity method income (net) in the Consolidated Statements of Income and the carrying value of the Affiliate is reported in Equity method investments in Affiliates (net) in the Consolidated Balance Sheets. Deferred taxes recorded on intangible assets upon acquisition of an Affiliate accounted for under the equity method are presented on a gross basis within Equity method investments in Affiliates (net) and Deferred income tax liability (net) in the Consolidated Balance Sheets. The Company’s share of income taxes incurred directly by Affiliates accounted for under the equity method is recorded in Income tax expense in the Consolidated Statements of Income. The Company periodically performs assessments to determine if the fair value of an investment may have declined below its related carrying value for its Affiliates accounted for under the equity method for a period that the Company considers to be other-than-temporary. Where the Company believes that such declines may have occurred, the Company determines the amount of impairment using valuation methods, such as discounted cash flow analyses. Impairments are recorded as an expense in Equity method income (net) to reduce the carrying value of the Affiliate to its fair value. 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 other 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 presented within 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.