Accrued Compensation and Benefits - Performance Allocations and Incentive Fee Related Compensation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Retirement Benefits [Abstract]
Realized	$ 50.0	$ 63.6	$ 245.7	$ 132.0
Unrealized	200.6	29.0	98.0	259.6
Total	$ 250.6	$ 92.6	$ 343.7	$ 391.6