Goodwill and Intangible Assets (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Amortization expense for intangible assets	$ 106	$ 82	$ 80
Acquisition of intangible assets	$ 120
Weighted-average amortization period (years)	10 years
Virginia Electric and Power Company
Goodwill [Line Items]
Amortization expense for intangible assets	$ 30	31	31
Acquisition of intangible assets	$ 52
Weighted-average amortization period (years)	8 years
Dominion Energy Gas Holdings, LLC
Goodwill [Line Items]
Amortization expense for intangible assets	$ 11	$ 11	$ 9
Acquisition of intangible assets	$ 7
Weighted-average amortization period (years)	29 years