Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
U.S. statutory rate	21.00%	21.00%	21.00%
Increases (reductions) resulting from:
State taxes, net of federal benefit	4.70%	5.60%	4.20%
AFUDC - equity	0.00%	(0.40%)	(0.10%)
Amortization of federal investment tax credits	(0.20%)	(0.60%)	(0.40%)
Reversal of excess deferred income taxes	(4.60%)	(8.10%)	(6.00%)
Changes in unrecognized tax benefits	0.00%	(15.80%)	(0.00%)
Prior period adjustments	0.00%	1.60%	0.00%
Other	(0.20%)	0.50%	0.10%
Effective tax rate	20.70%	3.80%	18.80%