Income Taxes (Schedule Of Income Tax Provision) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income before provision for income taxes	$ 141.6	$ 136.5	$ 134.7	$ 118.4	$ 125.9	$ 117.9	$ 117.4	$ 113.3	$ 531.2	$ 474.5	$ 420.9
Current provision for income taxes, Federal									157.2	127.9	90.9
Current provision for income taxes, State									15.8	10.6	7.3
Current provision for income taxes									173.0	138.5	98.2
Deferred provision for income taxes, Federal									22.4	33.7	52.0
Deferred provision for income taxes, State									1.8	1.9	4.1
Deferred provision for income taxes									24.2	35.6	56.1
Interest									1.2	0.7	0.4
Unrecognized Tax Benefits, Income Tax Penalties Expense									0.0	0.0	0.0
Interest and penalties expense (benefit)									1.2	0.7	0.4
Provision for income taxes									$ 198.4	$ 174.8	$ 154.7