Income Taxes (Schedule Of Reasons Behind Differences In Computation Of Total Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Schedule of Reasons Behind Differences in Computation of Total Income Taxes [Line Items]
Book income (loss) before income taxes	$ 956.4	$ 706.6	$ (31.3)
Tax expense (benefit) at statutory federal income tax rate, value	$ 200.8	$ 148.3	$ (6.6)
Tax expense (benefit) at statutory federal income tax rate, rate	21.00%	21.00%	21.00%
Increases (reductions) in taxes resulting from:
State income taxes, net of federal income tax benefit, value	$ 4.5	$ 14.1	$ (11.7)
State income taxes, net of federal income tax benefit, rate	0.50%	2.00%	37.40%
Amortization of regulatory liabilities, value	$ (38.5)	$ (39.1)	$ (38.4)
Amortization of regulatory liabilities, rate	(4.00%)	(5.50%)	122.70%
Fines and penalties, value	$ 0.3	$ 0.0	$ 11.8
Fines and penalties, rate	0.00%	0.00%	(37.70%)
Employee stock ownership plan dividends and other compensation, value	$ (1.2)	$ (1.2)	$ (1.3)
Employee stock ownership plan dividends and other compensation, rate	(0.10%)	(0.20%)	4.20%
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act, Amount	$ 0.0	$ 0.0	$ 23.3
State regulatory proceedings, rate	0.00%	0.00%	(74.50%)
Effective Income Tax Rate Reconciliation Tax Accrual Adjustments	$ 0.2	$ (0.1)	$ 8.9
Effective Income Tax Rate Reconciliation, Tax Credit, Amount	$ (2.3)	$ (2.1)	$ (2.5)
Effective Income Tax Rate Reconciliation, Tax Credit, Percent	(0.20%)	(0.30%)	(8.00%)
Other adjustments, value	$ 0.8	$ (2.1)	$ (0.6)
Other adjustments, rate	0.00%	(0.30%)	1.90%
Income Taxes	$ 164.6	$ 117.8	$ (17.1)
Income Taxes, rate	17.20%	16.70%	54.60%

Effective Income Tax Rate Reconciliation, Tax Accrual Adjustments, Amount

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