Income Taxes - Components of Income Before Tax and Benefit for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of income (loss) before income taxes
United States	$ (563.7)	$ (1,662.5)	$ (595.1)
Foreign	85.0	(31.7)	100.2
Net loss before income taxes	(478.7)	(1,694.2)	(494.9)
Current
U.S. Federal	10.2	(24.6)	(14.4)
U.S. State	(0.3)	(0.8)	0.3
Foreign	32.0	36.4	17.8
Total	41.9	11.0	3.7
Deferred
U.S. Federal	(129.5)	(287.4)	(234.6)
U.S. State	(8.5)	(22.0)	(21.2)
Foreign	(28.9)	(1.5)	(8.5)
Total	(166.9)	(310.9)	(264.3)
Total income tax benefit	$ (125.0)	$ (299.9)	$ (260.6)