Income Taxes (Schedule Of Reasons Behind Differences In Computation Of Total Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Reasons Behind Differences in Computation of Total Income Taxes [Line Items]
Book income before income taxes	$ 813.9	$ 956.4	$ 706.6
Tax expense (benefit) at statutory federal income tax rate, value	$ 170.8	$ 200.8	$ 148.3
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	$ 13.7	$ 4.5	$ 14.1
State income taxes, net of federal income tax benefit, rate	1.70%	0.50%	2.00%
Amortization of regulatory liabilities, value	$ (38.2)	$ (38.5)	$ (39.1)
Amortization of regulatory liabilities, rate	4.70%	4.00%	5.50%
Fines and penalties, value	$ 0.0	$ 0.3	$ 0.0
Fines and penalties, rate	0.00%	0.00%	0.00%
Employee stock ownership plan dividends and other compensation, value	$ (1.3)	$ (1.2)	$ (1.2)
Employee stock ownership plan dividends and other compensation, rate	(0.20%)	(0.10%)	(0.20%)
Effective Income Tax Rate Reconciliation Tax Accrual Adjustments	$ 0.0	$ 0.2	$ (0.1)
Effective Income Tax Rate Reconciliation, Tax Credit, Amount	$ (4.9)	$ (2.3)	$ (2.1)
Effective Income Tax Rate Reconciliation, Tax Credit, Percent	(0.60%)	(0.20%)	(0.30%)
Other adjustments, value	$ (0.6)	$ 0.8	$ (2.1)
Other adjustments, rate	0.10%	0.00%	0.30%
Income Taxes	$ 139.5	$ 164.6	$ 117.8
Income Taxes, rate	17.10%	17.20%	16.70%

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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