Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Regulatory assets:
Regulatory assets	$ 1,148	$ 1,002
Less: Current portion	305	136
Long-term regulatory assets	843	866
Regulatory liabilities:
Regulatory liabilities	1,184	1,170
Less: Current portion	63	78
Long-term regulatory liabilities	1,121	1,092
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	129	117
Cost-Recovery Clauses Regulatory Assets [Member]
Regulatory assets:
Regulatory assets	243	89
Capital Cost Recovery for Early Retired Assets [Member]
Regulatory assets:
Regulatory assets	508	518
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	22	22
Postretirement Benefits [Member]
Regulatory assets:
Regulatory assets	219	230
Asset Retirement Obligation [Member]
Regulatory assets:
Regulatory assets	12	11
Other [Member]
Regulatory assets:
Regulatory assets	15	15
Regulatory Tax Liability [Member] | Non-Current Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	638	638
Cost-Recovery Clauses - Deferred Balances Regulatory Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	26	16
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	472	468
Storm Reserve [Member]
Regulatory liabilities:
Regulatory liabilities	46	46
Other [Member]
Regulatory liabilities:
Regulatory liabilities	$ 2	$ 2