Investments - Investment Income (Details) - Consolidated Entity Excluding Consolidated Funds - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Net Investment Income [Line Items]
Investment income (loss)	$ 4.7	$ 6.6	$ 7.3	$ (7.1)
Realized and unrealized gains (losses) on other investments held at fair value
Net Investment Income [Line Items]
Investment income (loss)	3.5	6.0	4.9	(8.3)
Earnings from equity-accounted investment in Affiliate
Net Investment Income [Line Items]
Investment income (loss)	$ 1.2	$ 0.6	$ 2.4	$ 1.2