Equity (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Common stock, par value		$ 0
Common stock, shares authorized		50,000,000
Common stock, shares issued		40,300,000
Common stock, shares outstanding		40,300,000	40,300,000
Preferred stock, par value		$ 0
Preferred stock, shares authorized		20,000,000
Preferred stock, shares issued		1,000
Preferred stock, shares outstanding		1,000
Contributions from SCANA		$ 0	$ 838	$ 24
Dominion Energy
Class Of Stock [Line Items]
Contributions from SCANA			$ 835
Dominion Energy | Common Stock
Class Of Stock [Line Items]
Common stock issued to satisfy the settlement	$ 322
Dominion Energy | Common Stock | DESC Ratepayer Case
Class Of Stock [Line Items]
Common stock issued to satisfy the settlement		$ 322