Related-Party Transactions (Parenthetical) (Detail) - Virginia Electric and Power Company - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Capital expenditures	$ 3,138	$ 2,642	$ 2,228
Services provided by affiliates \| Affiliated Entity
Related Party Transaction [Line Items]
Capital expenditures	$ 141	$ 133	$ 145

The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration