Investments - Net Investment Gains (Losses) of Consolidated Funds (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Equity Method Investments and Joint Ventures [Abstract]
Gains (losses) from investments of Consolidated Funds	$ (5.6)	$ 94.2	$ 29.6	$ 26.4
Gains (losses) from liabilities of CLOs	46.3	(87.3)	28.2	(27.9)
Losses on other assets of CLOs	0.0	(0.2)	0.0	(0.2)
Total	$ 40.7	$ 6.7	$ 57.8	$ (1.7)