Income Taxes (Schedule Of Income Tax Provision) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income before provision for income taxes	$ 201.0	$ 198.4	$ 198.0	$ 157.7	$ 122.4	$ 160.1	$ 157.1	$ 144.2	$ 755.1	$ 583.8	$ 531.2
Current provision for income taxes, Federal									110.9	184.6	157.2
Current provision for income taxes, State									19.5	13.5	15.8
Current provision for income taxes									130.4	198.1	173.0
Deferred provision for income taxes, Federal									35.0	(88.4)	22.4
Deferred provision for income taxes, State									14.3	2.7	1.8
Deferred provision for income taxes									49.3	(85.7)	24.2
Interest									1.4	1.2	1.2
Unrecognized Tax Benefits, Income Tax Penalties Expense									0.0	0.0	0.0
Interest and penalties expense (benefit)									1.4	1.2	1.2
Provision for income taxes									$ 181.1	$ 113.6	$ 198.4