Income Taxes Income Taxes - Tax Cuts and Jobs Act (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax benefit resulting from impact of Tax Act	$ (57.7)	$ 0.0	$ 0.0
Charge related to the Transition Tax	32.5
Benefit from permanent rate reduction	$ 90.2