Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Income tax expense, decrease in deferred tax assets due to change in tax rate					$ 45.0
Income tax benefit, decrease in deferred tax liability due to change in tax rate					80.8
Income tax expense (benefit), net decrease in tax assets and liabilities due to change in tax rate					$ (35.8)
Effective income tax rate	14.00%	19.00%	17.00%	14.00%
Effective income tax rate without discrete tax benefit	13.00%	20.00%	16.00%	19.00%
Accounting Standards Update 2016-09
Operating Loss Carryforwards [Line Items]
Recorded tax expense (benefit) related to excess tax benefits on equity compensation	$ 0.2	$ (0.2)	$ 0.7	$ (1.7)