Investments - Schedule of Net Investment Earnings (Loss) (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]
Management fees	$ 14.5	$ 13.8	$ 41.4	$ 43.4
Performance fees	(3.4)	3.1	(18.5)	3.1
Investment income (loss)	(2.0)	0.0	(2.5)	0.0
Expenses and amortization of basis differences	(15.3)	(19.3)	(53.1)	(57.6)
Net investment income (loss)	$ (6.2)	$ (2.4)	$ (32.7)	$ (11.1)