Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Regulatory assets:
Regulatory assets	$ 1,048	$ 1,002
Less: Current portion	209	136
Long-term regulatory assets	839	866
Regulatory liabilities:
Regulatory liabilities	1,181	1,170
Less: Current portion	49	78
Long-term regulatory liabilities	1,132	1,092
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	119	117
Cost-Recovery Clauses Regulatory Assets [Member]
Regulatory assets:
Regulatory assets	142	89
Capital Cost Recovery for Early Retired Assets [Member]
Regulatory assets:
Regulatory assets	512	518
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	22	22
Postretirement Benefits [Member]
Regulatory assets:
Regulatory assets	225	230
Asset Retirement Obligation [Member]
Regulatory assets:
Regulatory assets	11	11
Other [Member]
Regulatory assets:
Regulatory assets	17	15
Regulatory Tax Liability [Member] | Non-Current Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	641	638
Cost-Recovery Clauses - Deferred Balances Regulatory Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	22	16
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	470	468
Storm Reserve [Member]
Regulatory liabilities:
Regulatory liabilities	46	46
Other [Member]
Regulatory liabilities:
Regulatory liabilities	$ 2	$ 2