Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective income tax rate (as percent)	23.00%	36.50%	26.30%	35.90%
U.S. Federal statutory rate (as percent)			21.00%
Income Tax [Line Items]
Tax expense related to the Tax Act of December 2017			$ (0.2)
Gross unrecognized tax benefits, including interest and penalties	$ 78.9		78.9		$ 66.5
Decrease in unrecognized tax benefits	$ 42.4		$ 42.4
Minimum
Income Tax [Line Items]
Expected annual effective income tax rate (as percent)			26.00%
Maximum
Income Tax [Line Items]
Expected annual effective income tax rate (as percent)			27.00%