Operating Segments (Narrative) (Detail) $ in Millions	3 Months Ended					12 Months Ended
	Dec. 31, 2019 USD ($) Segment	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) Segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Segment Reporting Information [Line Items]
Number of primary operating segments | Segment	1					1
Charge for refund of amounts from customers	$ 76			$ 73		$ 76	$ 73
Charge for refund of amounts from customers, after tax			$ 756
Litigation settlement expense, after tax	240	$ 75	118
Charge for utility plant but committed to forgo recovery, after tax			86
Charge related to a voluntary retirement program, after-tax		$ 47
Asset impairment charge			$ 105			576	1,376	$ 1,118
Asset impairment charge after-tax				$ 870	$ 3			690
Operating Segment | Corporate and Other
Segment Reporting Information [Line Items]
After- tax net expenses						1,600	917	690
Operating Segment | Dominion Energy South Carolina
Segment Reporting Information [Line Items]
Charge for refund of amounts from customers	1,000					1,000
Charge for refund of amounts from customers, after tax						756
Litigation settlement expense						590
Litigation settlement expense, after tax						444
Income tax related to regulatory assets acquired	194					194
Income tax related to regulatory assets acquired, after tax	$ 258					258
Charge for utility plant but committed to forgo recovery						114
Charge for utility plant but committed to forgo recovery, after tax						86
Merger-related costs						100
Merger-related costs, after tax						76
Charge related to a voluntary retirement program						79
Charge related to a voluntary retirement program, after-tax						59
Changes in unrecognized tax benefits						$ 66
Asset impairment charge							1,400	1,100
Asset impairment charge after-tax							$ 870	$ 690