Income Taxes (Schedule Of Income Tax Provision) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income before provision for income taxes	$ 216.1	$ 318.4	$ 127.8	$ (112.8)	$ 215.2	$ 219.1	$ 215.3	$ 206.3	$ 549.5	$ 855.9	$ 755.1
Current provision for income taxes, Federal									53.8	94.1	110.9
Current provision for income taxes, State									6.6	18.7	19.5
Current provision for income taxes									60.4	112.8	130.4
Deferred provision for income taxes, Federal									57.3	70.7	35.0
Deferred provision for income taxes, State									11.0	14.8	14.3
Deferred provision for income taxes									68.3	85.5	49.3
Interest									(0.2)	1.5	1.4
Unrecognized Tax Benefits, Income Tax Penalties Expense									0.0	0.0	0.0
Interest and penalties expense (benefit)									(0.2)	1.5	1.4
Provision for income taxes									$ 128.5	$ 199.8	$ 181.1