Income Taxes (Provision for Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 86.1	$ 106.0	$ 101.0
State	12.5	14.5	13.1
Foreign	15.0	9.7	3.6
Total current	113.6	130.2	117.7
Deferred:
Federal	43.8	(4.5)	(21.4)
State	0.9	(1.2)	(0.6)
Foreign	(1.4)	(0.4)	(0.3)
Total deferred	43.3	(6.1)	(22.3)
Total provision for income taxes	$ 156.9	$ 124.1	$ 95.4