Income Taxes (Schedule Of Income Tax Provision) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income before provision for income taxes	$ 215.2	$ 219.1	$ 215.3	$ 206.3	$ 201.0	$ 198.4	$ 198.0	$ 157.7	$ 855.9	$ 755.1	$ 583.8
Current provision for income taxes, Federal									94.1	110.9	184.6
Current provision for income taxes, State									18.7	19.5	13.5
Current provision for income taxes									112.8	130.4	198.1
Deferred provision for income taxes, Federal									70.7	35.0	(88.4)
Deferred provision for income taxes, State									14.8	14.3	2.7
Deferred provision for income taxes									85.5	49.3	(85.7)
Interest									1.5	1.4	1.2
Unrecognized Tax Benefits, Income Tax Penalties Expense									0.0	0.0	0.0
Interest and penalties expense (benefit)									1.5	1.4	1.2
Provision for income taxes									$ 199.8	$ 181.1	$ 113.6