Investments - Components of Net Investment Gains (Losses) of Consolidated Funds (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity Method Investments and Joint Ventures [Abstract]
Gains from investments of Consolidated Funds									$ 426.2	$ 857.7	$ 1,390.5
Gains (losses) from liabilities of CLOs									436.5	27.2	(695.1)
Gains on other assets of CLOs									1.7	2.1	1.3
Total	$ (71.4)	$ (31.3)	$ 461.6	$ 505.5	$ (107.5)	$ 125.5	$ 445.0	$ 424.0	$ 864.4	$ 887.0	$ 696.7