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Equity Method Investments in Affiliates - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Estimated Future Amortization Expense of Finite-Lived Intangibles
Net income	$ 63.5		$ 180.2		$ 103.4	$ 47.2
Acquired Client Relationships
Schedule of Equity Method Investments [Line Items]
Amortization expense during the period					55.7
Estimated Future Amortization Expense of Finite-Lived Intangibles
Finite-lived intangible, future amortization expense in 2020	60.0				60.0
Finite-lived intangible, future amortization expense in 2021	30.0				30.0
Finite-lived intangible, future amortization expense in 2022	30.0				30.0
Finite-lived intangible, future amortization expense in 2023	30.0				30.0
Finite-lived intangible, future amortization expense in 2024	20.0				20.0
Equity Method Investee
Estimated Future Amortization Expense of Finite-Lived Intangibles
Impairment expense		$ 140.0		$ 415.0
Average projected growth rate period		5 years		5 years
Average projected growth rate		(2.00%)		(13.00%)
Discount rate for assets based fees		11.00%		11.00%
Discount rate for performance fees		20.00%		20.00%
Market participant tax rate		25.00%		25.00%
Equity Method Investee | Acquired Client Relationships
Schedule of Equity Method Investments [Line Items]
Amortization expense during the period	36.9		38.9		76.2	62.1
Estimated Future Amortization Expense of Finite-Lived Intangibles
Finite-lived intangible, future amortization expense in 2020	150.0				150.0
Finite-lived intangible, future amortization expense in 2021	120.0				120.0
Finite-lived intangible, future amortization expense in 2022	50.0				50.0
Finite-lived intangible, future amortization expense in 2023	50.0				50.0
Finite-lived intangible, future amortization expense in 2024	50.0				50.0
Certain Affiliates
Estimated Future Amortization Expense of Finite-Lived Intangibles
Revenues	460.1		519.9		1,165.3	1,168.2
Net income	$ 128.5		$ 238.5		$ 555.6	$ 580.7

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