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Equity Method Investments in Affiliates - Additional Information (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |  |  |  |
Equity method investments in Affiliates (net) | $ 2,074.8 |  | $ 2,195.6 |  |  |  | $ 2,074.8 | $ 2,195.6 |
Other liabilities | 452.2 |  | 359.1 |  |  |  | 452.2 | 359.1 |
Equity method loss (net) |  |  |  |  |  |  | (43.4) | (338.0) | $ (0.2)
Equity Method Investee |  |  |  |  |  |  |  |  |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |  |  |  |
Impairment of equity method investment | $ 45.0 | $ 140.0 | $ 60.0 | $ 10.0 |  | $ 415.0 |  |  |
Fair value assumptions, average projected growth period | 5 years | 5 years |  |  |  | 5 years |  |  |
Fair value assumptions, average projected growth rate |  |  | 9.00% | (20.00%) |  | (13.00%) |  |  |
Fair value assumptions, discount rate for asset based fees |  |  | 11.00% | 11.00% |  | 11.00% |  |  |
Fair value assumptions, discount rate for performance based fees |  |  | 20.00% | 20.00% |  | 20.00% |  |  |
Fair value assumptions, market participant tax rate |  |  | 25.00% | 25.00% |  | 25.00% |  |  |
Equity method investments in Affiliates (net) | $ 2,074.8 |  | $ 2,195.6 |  |  |  | 2,074.8 | 2,195.6 | 2,791.0
Undistributed earnings from equity method affiliates | 170.6 |  |  |  |  |  | 170.6 |  |
Contingent payments due |  |  |  |  |  |  |  |  |
2021 | 35.0 |  |  |  |  |  | 35.0 |  |
2022 | 37.5 |  |  |  |  |  | 37.5 |  |
Equity Method Investee | Achievement of Specified Financial Targets |  |  |  |  |  |  |  |  |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |  |  |  |
Equity method investments in Affiliates (net) | 40.0 |  |  |  |  |  | 40.0 |  |
Other liabilities | $ 40.0 |  |  |  |  |  | 40.0 |  |
Equity Method Investee | Minimum |  |  |  |  |  |  |  |  |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |  |  |  |
Fair value assumptions, average projected growth rate |  | (2.00%) |  |  |  |  |  |  |
Fair value assumptions, discount rate for asset based fees | 11.00% | 11.00% |  |  |  |  |  |  |
Fair value assumptions, discount rate for performance based fees | 20.00% | 20.00% |  |  |  |  |  |  |
Fair value assumptions, market participant tax rate | 25.00% | 25.00% |  |  |  |  |  |  |
Equity Method Investee | Maximum |  |  |  |  |  |  |  |  |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |  |  |  |
Fair value assumptions, average projected growth rate | (5.00%) |  |  |  |  |  |  |  |
Acquired Client Relationships Under Equity Method Investments | Equity Method Investee |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |
Intangible amortization expense |  |  |  |  |  |  | 147.0 | $ 142.4 | $ 97.5
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |  |  |  |
Intangible future amortization expense in 2021 | $ 120.0 |  |  |  |  |  | 120.0 |  |
Intangible future amortization expense in 2022 | 50.0 |  |  |  |  |  | 50.0 |  |
Intangible future amortization expense in 2023 | 50.0 |  |  |  |  |  | 50.0 |  |
Intangible future amortization expense in 2024 | 50.0 |  |  |  |  |  | 50.0 |  |
Intangible future amortization expense in 2025 | $ 50.0 |  |  |  |  |  | $ 50.0 |  |
Non-US | Equity Method Investee |  |  |  |  |  |  |  |  |
Estimated Future Amortization Expense of Finite-Lived Intangibles |  |  |  |  |  |  |  |  |
Noncontrolling interest, sale of ownership percentage |  |  |  |  | 5.00% |  |  |  |
Payments to noncontrolling interests |  |  |  |  | $ 25.7 |  |  |  |

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