Equity (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Class Of Stock [Line Items]
Common stock, par value		$ 0		$ 0
Common stock, shares authorized		50,000,000		50,000,000
Common stock, shares issued		40,300,000		40,300,000
Common stock, shares outstanding		40,300,000		40,300,000
Preferred stock, par value		$ 0		$ 0
Preferred stock, shares authorized		20,000,000		20,000,000
Preferred stock, shares issued		1,000		1,000
Preferred stock, shares outstanding		1,000		1,000
Contributions from parent		$ 0	$ 825
Dominion Energy
Class Of Stock [Line Items]
Contributions from parent	$ 50		$ 825
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