Property, Plant and Equipment (Narrative) (Detail) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) MW	Sep. 30, 2019 USD ($)
Property Plant And Equipment [Line Items]
Impairment of assets and other charges		$ 1,151	$ 85	$ 1,963	$ 1,219
Dominion Energy
Property Plant And Equipment [Line Items]
Impairment of assets and other charges		665		665
Asset impairment charges after tax		293		293
Impairment of assets and other charges attributable to noncontrolling interest		267		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
Property Plant And Equipment [Line Items]
Anticipated projected cost		$ 41		$ 41
Aggregate generation capacity | MW				20