Income Taxes - Income Before Income Tax (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Domestic	$ 762.3	$ 608.3	$ 635.5
Foreign	78.2	52.4	37.7
Income before income taxes	$ 840.5	$ 660.7	$ 673.2