Accrued Compensation and Benefits - Performance Allocations and Incentive-Fee Related Compensation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Realized	$ 219.1	$ 363.8	$ 520.7
Unrealized	217.6	12.5	467.6
Total	$ 436.7	$ 376.3	$ 988.3