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Equity Method Investments in Affiliates - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Schedule of Equity Method Investments [Line Items]
Amortization expense during the period	$ 20.6	$ 29.6
Estimated Future Amortization Expense of Finite-Lived Intangibles
Equity method affiliates, revenue	617.0	590.5
Equity method affiliates, net income	382.8	328.7
Acquired Client Relationships
Schedule of Equity Method Investments [Line Items]
Amortization expense during the period	20.6
Estimated Future Amortization Expense of Finite-Lived Intangibles
Finite-lived intangible, future amortization expense in 2020	60.0
Finite-lived intangible, future amortization expense in 2021	30.0
Finite-lived intangible, future amortization expense in 2022	30.0
Finite-lived intangible, future amortization expense in 2023	30.0
Finite-lived intangible, future amortization expense in 2024	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	$ 39.3	$ 23.2
Estimated Future Amortization Expense of Finite-Lived Intangibles
Finite-lived intangible, future amortization expense in 2020	150.0
Finite-lived intangible, future amortization expense in 2021	120.0
Finite-lived intangible, future amortization expense in 2022	60.0
Finite-lived intangible, future amortization expense in 2023	50.0
Finite-lived intangible, future amortization expense in 2024	$ 40.0

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