Investments - Interest and Other Income of Consolidated Funds (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Equity Method Investments and Joint Ventures [Abstract]
Interest income from investments	$ 219.0	$ 217.0	$ 654.7	$ 653.0
Other income	40.4	17.1	88.0	75.5
Total	$ 259.4	$ 234.1	$ 742.7	$ 728.5