Regulatory - Schedule of Regulatory Assets and Regulatory Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Regulatory assets:
Regulatory assets	$ 488	$ 485
Less: Current portion	80	79
Long-term regulatory assets	408	406
Regulatory liabilities:
Regulatory liabilities	1,199	1,261
Less: Current portion	51	67
Long-term regulatory liabilities	1,148	1,194
Regulatory Tax Asset [Member]
Regulatory assets:
Regulatory assets	101	90
Cost-Recovery Clauses [Member]
Regulatory assets:
Regulatory assets	53	38
Environmental Remediation [Member]
Regulatory assets:
Regulatory assets	24	22
Postretirement Benefits [Member]
Regulatory assets:
Regulatory assets	290	309
Asset Retirement Obligation [Member]
Regulatory assets:
Regulatory assets	10	13
Other [Member]
Regulatory assets:
Regulatory assets	10	13
Regulatory Tax Liability [Member] \| Non-Current Liabilities [Member]
Regulatory liabilities:
Regulatory liabilities	663	691
Cost-Recovery Clauses [Member]
Regulatory liabilities:
Regulatory liabilities	18	23
Storm Reserve [Member]
Regulatory liabilities:
Regulatory liabilities	46	48
Accumulated Reserve - Cost of Removal [Member]
Regulatory liabilities:
Regulatory liabilities	469	498
Other [Member]
Regulatory liabilities:
Regulatory liabilities	$ 3	$ 1

Regulatory assets.

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Regulatory liabilities.

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

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The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.

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The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period.

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The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 210
-SubTopic 10
-Section S99
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