Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Regulatory assets:
Regulatory assets	$ 945	$ 988
Less: Current portion	104	161
Long-term regulatory assets	841	827
Regulatory liabilities:
Regulatory liabilities	880	795
Less: Current portion	188	94
Long-term regulatory liabilities	692	701
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	117	112
Cost-Recovery Clauses [Member]
Regulatory assets:
Regulatory assets	17	94
Capital Cost Recovery for Early Retired Assets [Member]
Regulatory assets:
Regulatory assets	513	507
Postretirement Benefits [Member]
Regulatory assets:
Regulatory assets	234	236
Storm Reserve [Member]
Regulatory assets:
Regulatory assets	35	7
Other [Member]
Regulatory assets:
Regulatory assets	29	32
Regulatory Tax Liability [Member] | Non-Current Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	445	477
Cost-recovery Clauses - Deferred Balances [Member]
Regulatory liabilities:
Regulatory liabilities	75	20
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	302	271
Other [Member]
Regulatory liabilities:
Regulatory liabilities	$ 58	$ 27