Derivatives and Hedge Accounting Activities (Schedule of Offsetting Liabilities) (Parenthetical) (Detail) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Offsetting Liabilities [Line Items]
Derivative liabilities, not subject to a master netting or similar arrangement	$ 0	$ 0
Virginia Electric and Power Company
Offsetting Liabilities [Line Items]
Derivative liabilities, not subject to a master netting or similar arrangement	$ 55,000,000	$ 26,000,000

Fair value of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, not subject to a master netting arrangement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-SubTopic 20
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483466/210-20-50-3

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483444/210-20-55-22

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant