Investments - Schedule of Net Investment Earnings (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Equity Method Investments and Joint Ventures [Abstract]
Management fees	$ 20.9	$ 14.5	$ 62.1	$ 41.4
Performance fees	37.9	(3.4)	47.6	(18.5)
Investment income (loss)	6.4	(2.0)	10.8	(2.5)
Expenses and amortization of basis differences	(17.9)	(15.3)	(52.1)	(53.1)
Net investment income (loss)	$ 47.3	$ (6.2)	$ 68.4	$ (32.7)