Income Taxes (Schedule of Reconciliation of the U.S. Federal Statutory Rate to Effective Tax Rate) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
U.S. federal statutory rate	35.00%	35.00%	35.00%	35.00%
State income taxes	1.90%	1.70%	1.80%	1.80%
Excess tax benefits from stock-based compensation plans	(0.00%)	(0.00%)	(0.50%)	(0.00%)
Other	0.20%	0.40%	0.20%	0.30%
Effective tax rate	37.10%	37.10%	36.50%	37.10%
Excess tax benefits			$ 2.5	$ 27.2