Investments - Principal Investments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total	$ 1,699.4	$ 2,443.6
Corporate Private Equity
Segment Reporting Information [Line Items]
Total	428.1	420.1
Real Assets
Segment Reporting Information [Line Items]
Total	582.7	601.7
Global Credit
Segment Reporting Information [Line Items]
Total	646.4	1,299.6
Investment Solutions
Segment Reporting Information [Line Items]
Total	$ 42.2	122.2
Investment Solutions | Investments deconsolidated during 2020
Segment Reporting Information [Line Items]
Total		$ 66.0