Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Regulatory assets:
Regulatory assets	$ 1,002	$ 485
Less: Current portion	136	79
Long-term regulatory assets	866	406
Regulatory liabilities:
Regulatory liabilities	1,170	1,261
Less: Current portion	78	67
Long-term regulatory liabilities	1,092	1,194
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	117	90
Cost-Recovery Clauses [Member]
Regulatory assets:
Regulatory assets	89	38
Capital Cost Recovery for Early Retired Assets [Member]
Regulatory assets:
Regulatory assets	518	0
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	22	22
Postretirement Benefits [Member]
Regulatory assets:
Regulatory assets	230	309
Asset Retirement Obligation [Member]
Regulatory assets:
Regulatory assets	11	13
Other [Member]
Regulatory assets:
Regulatory assets	15	13
Regulatory Tax Liability [Member] | Non-Current Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	638	691
Cost-recovery Clauses - Deferred Balances [Member]
Regulatory liabilities:
Regulatory liabilities	16	23
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	468	498
Storm Reserve [Member]
Regulatory liabilities:
Regulatory liabilities	46	48
Other [Member]
Regulatory liabilities:
Regulatory liabilities	$ 2	$ 1