Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Regulatory assets:
Regulatory assets	$ 941	$ 988
Less: Current portion	109	161
Long-term regulatory assets	832	827
Regulatory liabilities:
Regulatory liabilities	821	795
Less: Current portion	91	94
Long-term regulatory liabilities	730	701
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	113	112
Cost-Recovery Clauses [Member]
Regulatory assets:
Regulatory assets	46	94
Capital Cost Recovery for Early Retired Assets [Member]
Regulatory assets:
Regulatory assets	514	507
Postretirement Benefits [Member]
Regulatory assets:
Regulatory assets	236	236
Storm Reserve [Member]
Regulatory assets:
Regulatory assets	2	7
Other [Member]
Regulatory assets:
Regulatory assets	30	32
Regulatory Tax Liability [Member] | Non-Current Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	474	477
Cost-recovery Clauses - Deferred Balances [Member]
Regulatory liabilities:
Regulatory liabilities	14	20
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	300	271
Other [Member]
Regulatory liabilities:
Regulatory liabilities	$ 33	$ 27