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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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