Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Detail)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
U.S. statutory rate	21.00%	21.00%	21.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	4.10%	4.70%	5.60%
AFUDC - equity	0.00%	0.00%	(0.40%)
Amortization of federal investment tax credits	(0.30%)	(0.20%)	(0.60%)
Reversal of excess deferred income taxes	(4.70%)	(4.60%)	(8.10%)
Changes in unrecognized tax benefits	(2.20%)	0.00%	(15.80%)
Prior period adjustments	0.00%	0.00%	1.60%
Other	(0.20%)	(0.20%)	0.50%
Effective tax rate	17.70%	20.70%	3.80%