Segment Reporting - Reconciliation of Fund Level Fee Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Total Reportable Segments
Segment Reporting Information [Line Items]
Fund management fees	$ 411.9	$ 388.3
Adjustments
Segment Reporting Information [Line Items]
Adjustments	(30.9)	(32.4)
Fund management fees
Segment Reporting Information [Line Items]
Fund management fees	381.0	355.9
Fund management fees | Total Reportable Segments
Segment Reporting Information [Line Items]
Fund management fees	392.2	381.5
Fund management fees | Adjustments
Segment Reporting Information [Line Items]
Fund management fees	$ (5.8)	$ (5.2)