Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Contingency [Line Items]
Employee service share-based compensation, recognition of excess tax benefits				$ 1.8
Income tax calculated at 35% federal statutory rate	35.00%	35.00%	35.00%	35.00%
Current income tax benefit		$ 15.5
Tax benefit related to prior years		$ 12.5
Unrecognized tax benefit more likely than not percentage threshold			50.00%
Unrecognized tax benefits	$ 82.3		$ 82.3
Unrecognized tax benefits that would impact effective tax rate	66.1		66.1
Interest expense or penalties, uncertain tax positions			0.6	$ 0.5
Accrued interest, uncertain tax positions	$ 1.3		$ 1.3		$ 0.7
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Earliest year subject to examination			2000