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Equity Method Investments in Affiliates - Additional Information (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Jun. 30, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Intangible future amortization expense in 2022 |  | $ 30,000,000 |  |  |  |  |  | $ 30,000,000 |  |  |
Intangible future amortization expense in 2023 |  | 75,000,000 |  |  |  |  |  | 75,000,000 |  |  |
Impairment of equity method investment |  |  |  |  |  |  |  | 0 |  |  |
Equity method investments in affiliates |  | 2,195,600,000 |  |  |  | $ 2,791,000,000.0 |  | 2,195,600,000 |  | $ 2,791,000,000.0 |
Undistributed earnings from equity method affiliates |  | 115,000,000.0 |  |  |  |  |  | 115,000,000.0 |  |  |
Equity method investment, revenue | [1] |  |  |  |  |  |  | 2,760,900,000 |  | 3,231,700,000 | $ 3,126,300,000
Equity method investment, net income |  |  |  |  |  |  |  | 1,061,300,000 | [1] | 1,286,100,000 | 2,182,700,000
Assets |  | 2,718,500,000 |  |  |  | 2,730,400,000 |  | 2,718,500,000 |  | 2,730,400,000 |
Liabilities and Non-controlling interests |  | 1,212,700,000 |  |  |  | 1,235,100,000 |  | 1,212,700,000 |  | 1,235,100,000 |
U.S. Alternative Credit Affiliate |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Impairment of equity method investment |  |  |  |  | $ 415,000,000.0 |  |  |  |  |  |
Fair value assumptions, average projected growth rate |  |  |  |  | (13.00%) |  |  |  |  |  |
Fair value assumptions, discount rate for asset based fees |  |  |  |  | 11.00% |  |  |  |  |  |
Fair value assumptions, discount rate for performance based fees |  |  |  |  | 20.00% |  |  |  |  |  |
Fair value assumptions, market participant tax rate |  |  |  |  | 25.00% |  |  |  |  |  |
Fair value assumptions, average projected growth period |  |  |  |  | 5 years |  |  |  |  |  |
U.S. Alternative Affiliate |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Impairment of equity method investment |  | $ 60,000,000.0 | $ 10,000,000.0 |  |  |  |  |  |  |  |
Fair value assumptions, average projected growth rate |  | 9.00% | (20.00%) |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Equity method investments in affiliates |  | $ 2,195,600,000 |  |  |  | 2,791,000,000.0 |  | 2,195,600,000 |  | 2,791,000,000.0 | 3,304,700,000
Equity method investment, revenue |  |  |  |  |  |  |  | 844,800,000 |  |  |
Equity method investment, net income |  |  |  |  |  |  |  | 228,500,000 |  |  |
Assets |  | 392,900,000 |  |  |  |  |  | 392,900,000 |  |  |
Liabilities and Non-controlling interests |  | 299,800,000 |  |  |  |  |  | 299,800,000 |  |  |
Equity method investment, cash flows from operating activities |  |  |  |  |  |  |  | 308,700,000 |  |  |
Equity method investment, cash flows used in investing activities |  |  |  |  |  |  |  | 7,400,000 |  |  |
Equity method investment, cash flows used in financing activities |  |  |  |  |  |  |  | 313,100,000 |  |  |
Equity Method Investee | Non-U.S. Alternative Investment |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Impairment of equity method investment |  |  |  |  |  | $ 240,000,000.0 | $ 33,300,000 |  |  |  |
Equity method investments in affiliates |  |  |  |  |  |  | $ 0 |  |  |  |
Fair value assumptions, average projected growth rate |  |  |  |  |  | 2.50% |  |  |  |  |
Fair value assumptions, discount rate for asset based fees |  |  |  |  |  | 11.00% |  |  |  |  |
Fair value assumptions, discount rate for performance based fees |  |  |  |  |  | 20.00% |  |  |  |  |
Fair value assumptions, market participant tax rate |  |  |  |  |  | 25.00% |  |  |  |  |
Acquired Client Relationships Under Equity Method Investments |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Intangible amortization expense |  |  |  |  |  |  |  | 142,400,000 |  | $ 97,500,000 | $ 106,100,000
Intangible future amortization expense in 2020 |  | 130,000,000 |  |  |  |  |  | 130,000,000 |  |  |
Intangible future amortization expense in 2022 |  | 75,000,000 |  |  |  |  |  | 75,000,000 |  |  |
Intangible future amortization expense in 2023 |  | 75,000,000 |  |  |  |  |  | 75,000,000 |  |  |
Intangible future amortization expense in 2024 |  | $ 75,000,000 |  |  |  |  |  | $ 75,000,000 |  |  |
Non-US | Equity Method Investee |  |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |  |
Noncontrolling interest, sale of ownership percentage |  | 5.00% |  | 5.00% |  |  |  | 5.00% |  |  |
Payments to noncontrolling interests |  |  |  | $ 25,700,000 |  |  |  |  |  |  |
Ownership percentage held by minority interest in affiliated |  | 14.00% |  |  |  |  |  | 14.00% |  |  |
[1] | Revenue and net income include asset and performance based fees, the impact of consolidated sponsored investment products and investments in new Affiliates for the full-year, regardless of the date of the Company’s investment.

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