Asset Retirement Obligations (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019		Mar. 31, 2020
Asset Retirement Obligations [Line Items]
Asset retirement obligation, liabilities incurred			$ 67	$ 2,413	[1]
Nuclear decommissioning trust funds			6,900	6,192
Dominion Energy
Asset Retirement Obligations [Line Items]
Asset retirement obligation, liabilities incurred			1,900	1,700
D Virginia Electric And Power Company | Future Decommissioning Of Nuclear Facilities
Asset Retirement Obligations [Line Items]
Asset retirement obligation, liabilities incurred			900	800
D Virginia Electric And Power Company | D Cost Of Landfills And Beneficial Reuse
Asset Retirement Obligations [Line Items]
Asset retirement obligation, liabilities incurred			2,800	2,600
Virginia Electric and Power Company
Asset Retirement Obligations [Line Items]
Asset retirement obligation, liabilities incurred			48	2,408	[1]
Nuclear decommissioning trust funds			3,197	$ 2,881
Other deferred charges and other assets						$ 185
Virginia Electric and Power Company | Other Operations and Maintenance
Asset Retirement Obligations [Line Items]
Asset retirement obligation, liabilities incurred	$ 113	$ 81
ARO incurred, after tax	84	$ 60
Virginia Electric and Power Company | Cost of Landfills and Beneficial Reuse
Asset Retirement Obligations [Line Items]
Asset retirement obligation, liabilities incurred	2,400
Virginia Electric and Power Company | Increase In Property Plant And Equipment
Asset Retirement Obligations [Line Items]
Asset retirement obligation, liabilities incurred	1,300
Virginia Electric and Power Company | Future Ash Pond and Landfill Closure Costs
Asset Retirement Obligations [Line Items]
Asset retirement obligation, liabilities incurred	$ 202
Virginia Electric and Power Company | Post Closure Monitoring Costs
Asset Retirement Obligations [Line Items]
Asset retirement obligation, liabilities incurred			$ 140

[1] Reflects future ash pond and landfill closure costs at certain utility generation facilities. See discussion below.