Income Taxes (Reconciliation of Income Tax Rate) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Provision at the U.S. statutory rate of 21% (35% for 2017, 2016)	$ 98.3	$ 162.4	$ 141.0
U.S. statutory rate (as a percent)	21.00%	35.00%	35.00%
Increase (reduction) in tax expense resulting from:
State income tax, net of federal income tax benefit	$ 15.5	$ 9.2	$ 12.8
Domestic manufacturing deduction	0.0	(9.6)	(9.2)
Tax credits, net of unrecognized tax benefits	(2.5)	(8.6)	(27.9)
Change in unrecognized tax benefits	0.4	(0.1)	(0.3)
Change in valuation allowance	5.0	6.4	(4.3)
Foreign taxes at rates other than U.S. statutory rate	(3.2)	(9.0)	(1.3)
Deemed inclusions	3.9	0.3	16.9
Change in rates from the Tax Act & other law changes	1.9	31.8	(0.6)
Excess tax benefits from stock-based compensation	(10.5)	(23.6)	0.0
Miscellaneous other	(1.2)	(2.3)	(3.0)
Total provision for income taxes	$ 107.6	$ 156.9	$ 124.1