Income Taxes (Schedule Of Reconciliation Of Income Taxes To Statutory Rate) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense based on the U.S. statutory tax rate		$ 42.5	$ 57.5	$ 84.0
State income taxes, net of federal benefit		8.6	8.3	3.0
Effect of U.S. tax law change	$ (88.9)	0.0	0.0	(88.9)
Federal credits		(2.3)	(2.0)	(1.0)
Other, net		(1.2)	(3.5)	(2.3)
Total		$ 47.6	$ 60.3	$ (5.2)