Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Income Taxes
Effective income tax rate (as a percent)	29.60%	27.30%	24.90%	29.10%
Recognized discrete tax expense (Benefit), net	$ (19.2)	$ 1.9	$ (56.0)	$ 16.3
Valuation allowance on deferred tax asset	39.0		$ 39.0		$ 74.0
Decrease in valuation allowance	$ 17.0