Acquisitions and Dispositions (Schedule of Results of Operations Reported As Discontinued Operations) (Detail) - Dominion Energy Gas Holdings, LLC - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Net income (loss) from discontinued operations	$ 0	$ 26	$ 0	$ 80
East Ohio
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Operating revenue		154		383
Depreciation and amortization		22		43
Other operating expenses		128		277
Other income		18		37
Interest and related charges		8		18
Income tax expense		3		17
Net income (loss) from discontinued operations		11		65
DGP
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Operating revenue		34		79
Depreciation and amortization		1		2
Other operating expenses		12		56
Income tax expense		6		6
Net income (loss) from discontinued operations		$ 15		$ 15