Property, Plant and Equipment (Narrative) (Detail) $ in Millions	1 Months Ended			2 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017	Feb. 28, 2021 USD ($) MW	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Oct. 31, 2018 USD ($)
Property Plant And Equipment [Line Items]
Impairment of assets and other charges					$ 2,105	$ 1,520	$ 12
Dominion Energy
Property Plant And Equipment [Line Items]
Impairment of assets and other charges					665
Asset impairment charges after tax					293
Impairment of assets and other charges attributable to noncontrolling interest					267
Property, plant and equipment down to estimated fair value					$ 1,400
Wexpro | Natural Gas Gathering Systems | Colorado, Utah and Wyoming
Property Plant And Equipment [Line Items]
Payments to acquire existing natural gas gathering systems	$ 38
Acquisition of Solar Project at Schools in Virginia | Subsequent Event
Property Plant And Equipment [Line Items]
Anticipated projected cost				$ 61
Aggregate generation capacity | MW				30
Retail Energy Marketing Operations | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Property Plant And Equipment [Line Items]
Gain on sale						65
After tax gain on sale						$ 49
Commission receivable term			10 years
Retail Energy Marketing Operations | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Second Phase of Agreements to Sell Certain Assets
Property Plant And Equipment [Line Items]
Amount of consideration								$ 63
Fairless and Manchester
Property Plant And Equipment [Line Items]
Amount of consideration		$ 1,200					$ 1,200
Gain on sale of equity method investment		210
Gain on sale of equity method investments, net of tax		$ 198