Income Taxes (Provision for Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 128.9	$ 358.3	$ 299.5
State	46.9	48.4	34.6
Deferred:
Federal	121.5	(388.1)	44.9
State	30.6	9.1	2.3
State deferred benefit - change in valuation allowance	(4.5)	9.6	(1.4)
Uncertain tax positions and interest, and other	(40.1)	(34.2)	(27.2)
Provision for income taxes	$ 283.3	$ 3.1	$ 352.7