Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective tax rates	3.00%	20.00%
Income Tax Contingency [Line Items]
Unrecognized tax benefits	$ 47.8		$ 42.9
Reduction in provision for income taxes due to impact of effective tax rate	44.5
Deferred tax assets classified as other non-current assets	500.6		478.3
Deferred tax assets, valuation allowance	71.0		$ 49.4
Other Noncurrent Liabilities
Income Tax Contingency [Line Items]
Increase in unrecognized tax benefits is reasonably possible	25.4
Other Noncurrent Assets
Income Tax Contingency [Line Items]
Unrecognized tax benefits	22.4
Accounting Standards Update 2016-09
Income Tax Contingency [Line Items]
Effective income tax rate reconciliation, share-based compensation, excess tax benefit	$ 60.7	$ 36.0