Investments - Investment Components of Accrued Performance Fees (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Accrued performance allocations	$ 4,184.2	$ 3,855.6
Corporate Private Equity
Segment Reporting Information [Line Items]
Accrued performance allocations	2,820.2	2,107.5
Real Assets
Segment Reporting Information [Line Items]
Accrued performance allocations	523.1	764.4
Global Credit
Segment Reporting Information [Line Items]
Accrued performance allocations	86.5	136.9
Investment Solutions
Segment Reporting Information [Line Items]
Accrued performance allocations	$ 754.4	$ 846.8