Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Effective tax rates	20.00%	35.00%	25.00%	37.00%
Income Tax Contingency [Line Items]
Unrecognized tax benefits	$ 22.4		$ 22.4		$ 17.1
Reduction in provision for income taxes due to impact of effective tax rate	17.4		17.4
Deferred tax assets classified as other non-current assets	213.8		213.8		$ 180.6
Income tax benefits attributable to the exercise of employee stock options recorded directly to Additional paid-in-capital	13.3	$ 39.1	24.6	$ 67.9
Increase in unrecognized tax benefits is reasonably possible	18.4		18.4
Accrued Expenses
Income Tax Contingency [Line Items]
Unrecognized tax benefits	$ 4.0		$ 4.0