Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Regulatory assets:
Regulatory assets	$ 1,116	$ 1,552
Less: Current portion	227	361
Long-term regulatory assets	889	1,191
Regulatory liabilities:
Regulatory liabilities	813	1,140
Less: Current portion	86	85
Long-term regulatory liabilities	727	1,055
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	111	124
Cost-Recovery Clauses [Member]
Regulatory assets:
Regulatory assets	199	525
Capital Cost Recovery for Early Retired Assets [Member]
Regulatory assets:
Regulatory assets	499	497
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	0	20
Postretirement Benefits [Member]
Regulatory assets:
Regulatory assets	238	272
Asset Retirement Obligation [Member]
Regulatory assets:
Regulatory assets	11	13
Storm Reserve [Member]
Regulatory assets:
Regulatory assets	39	76
Other [Member]
Regulatory assets:
Regulatory assets	19	25
Regulatory Tax Liability [Member] | Non-Current Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	478	601
Cost-recovery Clauses - Deferred Balances [Member]
Regulatory liabilities:
Regulatory liabilities	23	30
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	288	498
Other [Member]
Regulatory liabilities:
Regulatory liabilities	$ 24	$ 11