Income Taxes - Income Tax Expense by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 192.6	$ 258.9	$ 295.6
State	43.3	29.8	34.9
Foreign	17.7	21.3	16.8
Total current	253.6	310.0	347.3
Deferred:
Domestic	(52.7)	(167.6)	(90.5)
Foreign	(3.4)	(4.8)	(8.7)
Total deferred	(56.1)	(172.4)	(99.2)
Income tax expense	$ 197.5	$ 137.6	$ 248.1