Income Taxes (Schedule Of Income Tax Provision) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Income before provision for income taxes	$ 125.9	$ 117.9	$ 117.4	$ 113.3	$ 116.4	$ 115.3	$ 109.2	$ 80.0	$ 474.5	$ 420.9	$ 398.2
Current provision for income taxes, Federal									127.9	90.9	128.4
Current provision for income taxes, State									10.6	7.3	7.4
Current provision for income taxes									138.5	98.2	135.8
Deferred provision for income taxes, Federal									33.7	52.0	8.7
Deferred provision for income taxes, State									1.9	4.1	0.1
Deferred provision for income taxes									35.6	56.1	8.8
Interest									0.7	0.4	0.5
Unrecognized Tax Benefits, Income Tax Penalties Expense									0.0	0.0	0.0
Interest and penalties expense (benefit)									0.7	0.4	0.5
Provision for income taxes									$ 174.8	$ 154.7	$ 145.1