Summary of Significant Accounting Policies (Schedule of Weighted Average Depreciation Rates) (Detail)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	[1]
Generation [Member]
Composite weighted average depreciation rates for utility plant	2.33%	2.34%	2.46%
Transmission [Member]
Composite weighted average depreciation rates for utility plant	2.54%	2.36%	2.56%
Distribution [Member]
Composite weighted average depreciation rates for utility plant	2.57%	2.59%	2.48%
Storage [Member]
Composite weighted average depreciation rates for utility plant	2.83%	2.93%	2.85%
General and other [Member]
Composite weighted average depreciation rates for utility plant	3.16%	3.35%	2.27%

[1] In 2021, a change in depreciation rates was approved in connection with the settlement of the electric base rate case, which resulted in a decrease to depreciation expense of $6 million for the year ended December 31, 2021, and $12 million annually thereafter.