Equity (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended
	Feb. 28, 2019	Mar. 31, 2020	Mar. 31, 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
Contribution from parent		$ 0	$ 675
Dominion Energy
Class Of Stock [Line Items]
Contribution from parent	$ 675