Acquisitions and Dispositions (Acquisition of SCANA) (Narrative) (Detail) - USD ($) shares in Millions, $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Jan. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Business Acquisition And Dispositions [Line Items]
Stock issued during period for acquisition, value						$ 6,818
Impairment of assets and other charges		$ 1,151	$ 85		$ 1,963	1,219
SCANA
Business Acquisition And Dispositions [Line Items]
Stock issued during period for acquisition, shares	95.6
Stock issued during period for acquisition, value	$ 6,800
Common stock agreed to be issued, percentage	0.669%
Total outstanding debt	$ 6,900
Impairment of assets and other charges		44	38		44	316
Impairment of assets and other charges, after tax		$ 33	28		$ 33	236
SCANA | NND Project
Business Acquisition And Dispositions [Line Items]
Property, plant and equipment	$ 105
Impairment of assets and other charges						105
Impairment of assets and other charges, after tax						79
SCANA | Dominion Energy South Carolina Inc
Business Acquisition And Dispositions [Line Items]
Period to provide refund to customer				11 years
Charge for refund of amounts from customers			1,000	$ 1,000		1,000
After tax charge in statements of income						756
SCANA | Dominion Energy South Carolina Inc | NND Project
Business Acquisition And Dispositions [Line Items]
Income tax regulatory assets			$ 264			264
Impairment of assets and other charges						$ 198