Income Taxes - Effective Tax Rate and Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Uncertain tax positions
Effective tax rate (as a percent)	17.10%	22.30%	16.90%	17.50%
Amount of unrecognized tax benefits	$ 18.8		$ 18.8		$ 22.3
Net, current activity			(3.5)
Gross accrued interest and penalties on unrecognized tax benefits	1.7		1.7		2.5
Unrecognized income tax benefits that, if recognized, would affect the effective tax rates	19.3		19.3		23.5
Unrecognized income tax benefits that, if recognized, would affect the effective tax rates , interest and penalties	1.0		1.0		$ 1.7
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 0.0		$ 0.0