Investments - Schedule of Income (Loss) from Equity-Method Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Income (loss) from equity investments	$ 9.4	$ (8.3)	$ 14.2
Corporate Private Equity
Schedule of Investments [Line Items]
Income (loss) from equity investments	28.9	53.8	59.2
Global Market Strategies
Schedule of Investments [Line Items]
Income (loss) from equity investments	(0.9)	1.3	4.6
Real Assets
Schedule of Investments [Line Items]
Income (loss) from equity investments	$ (18.6)	$ (63.4)	$ (49.6)