Income Taxes - Components of Income Tax Expense (Details 5) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current:
Federal	$ 0	$ (3.4)	$ 0
State	(1.1)	0.2	1.0
Foreign	2.1	1.9	1.9
Noncontrolling interests	0	0	17.6
Deferred:
Federal	7.7	14.0	31.5
State	0.2	1.2	2.8
Amount allocated to other comprehensive income	0	(22.7)	0
Change in valuation allowance on beginning-of-the-year deferred tax assets	(1.2)	(1.6)	735.2
Income tax expense (benefit)	$ 7.7	$ (10.4)	$ 790.0