Fair Value Measurements and the Fair Value Option - Schedule of Changes in Level 3 Investments (Details) - Equity Method Investments [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 186.6	$ 78.5	$ 85.9	$ 81.1
Unrealized gains	5.9	0.0	24.1	0.0
Unrealized losses	0.0	0.0	(0.1)	0.0
Realized Gains	5.2	0.0	5.2	0.0
Contributions	16.5	16.9	107.7	19.3
Distributions	(8.1)	(5.0)	(16.4)	(10.0)
Other	0.0	0.0	(0.3)	0.0
Ending balance	$ 206.1	$ 90.4	$ 206.1	$ 90.4