Equity (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2025	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Class Of Stock [Line Items]
Common stock, par value
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
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		$ 250	$ 0
Dominion Energy
Class Of Stock [Line Items]
Contributions from parent	$ 250