Significant Accounting Policies (Narrative) (Detail)	1 Months Ended						12 Months Ended
	Nov. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	May 31, 2019 USD ($)	Mar. 31, 2019 USD ($) Facility MW	Jan. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) MWh $ / shares		Dec. 31, 2019 USD ($) MWh		Dec. 31, 2018 USD ($) $ / shares	Jan. 01, 2019 USD ($)
Significant Accounting Policies [Line Items]
Accrued unbilled revenue							$ 1,100,000,000		$ 829,000,000
Margin deposit assets							19,000,000		42,000,000
Margin liabilities							5,000,000		2,000,000
Capitalized interest costs and Capitalized interest costs and AFUDC							103,000,000		78,000,000		$ 109,000,000
Impairment of assets and other charges							$ 2,105,000,000		$ 1,520,000,000		12,000,000
Finite Lived Intangible Asset Useful Life							30 years
Estimated proved developed or proved gas and oil reserves rate per unit | MWh							1.97		1.80
Retained earnings							$ 4,189,000,000		$ 7,576,000,000
Net unrealized gains on equity securities previously classified as cost method investments											36,000,000
Net unrealized gains on equity securities previously classified as cost method investments, after tax											22,000,000
Net unrealized losses in other income											190,000,000
Net unrealized losses in other income, after tax											$ 142,000,000
Gain per share from unrealized loss on securities | $ / shares											$ 0.22
Operating lease assets							564,000,000	[1]	462,000,000	[1]		$ 504,000,000
Operating lease liability							570,000,000
Tax reform, reclassification of tax benefit from AOCI to retained earnings											$ 289,000,000
Discontinued Operations | GT&S and Q-Pipe Transactions
Significant Accounting Policies [Line Items]
Operating lease assets							43,000,000
Operating lease liability							$ 43,000,000
Current Regulatory Liabilities
Significant Accounting Policies [Line Items]
Net unrealized gains on equity securities previously classified as cost method investments											33,000,000
Retained Earnings
Significant Accounting Policies [Line Items]
Net unrealized gains on equity securities previously classified as cost method investments											3,000,000
Accounting Standards Update 2014-09
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]							true
Change in Accounting Principle, Accounting Standards Update, Adoption Date							Jan. 01, 2018
Accounting Standards Update 2014-09 | Cumulative-effect of Changes in Accounting Principles
Significant Accounting Policies [Line Items]
Retained earnings											3,000,000
Accounting Standards Update 2016-13
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]							true
Change in Accounting Principle, Accounting Standards Update, Adoption Date							Jan. 01, 2018
Accounting Standards Update 2016-13 | Cumulative-effect of Changes in Accounting Principles
Significant Accounting Policies [Line Items]
Unrealized gains reclassified from AOCI to retained earnings											1,100,000,000
Unrealized gains reclassified from AOCI to retained earnings after-tax											$ 734,000,000
Accounting Standards Update 2016-02
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]							true
Change in Accounting Principle, Accounting Standards Update, Adoption Date							Jan. 01, 2019
Accounting Standards Update 2017-05
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]							true
Change in Accounting Principle, Accounting Standards Update, Adoption Date							Jan. 01, 2018
Accounting Standards Update 2017-05 | Cumulative-effect of Changes in Accounting Principles
Significant Accounting Policies [Line Items]
Retained earnings												127,000,000
Accounting Standards Update 2018-02
Significant Accounting Policies [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]							true
Change in Accounting Principle, Accounting Standards Update, Adoption Date							Jan. 01, 2018
Change in Depreciation Rates from New Depreciation Study
Significant Accounting Policies [Line Items]
Increase in EPS | $ / shares							$ 0.03				$ 0.07
Change in Depreciation Rates from New Depreciation Study | Merchant generation assets
Significant Accounting Policies [Line Items]
Increase (decrease) in depreciation expense											$ (30,000,000)
Increase (decrease) in depreciation expense, after tax											(23,000,000)
Impairment of Assets and Other Charges
Significant Accounting Policies [Line Items]
Impairment of assets and other charges			$ 26,000,000
Asset impairment charges after tax			19,000,000
Maximum
Significant Accounting Policies [Line Items]
Lessee Operating Lease Renewal Term							70 years
Minimum
Significant Accounting Policies [Line Items]
Lessee Operating Lease Renewal Term							1 year
Virginia Electric and Power Company
Significant Accounting Policies [Line Items]
Accrued unbilled revenue							$ 740,000,000		512,000,000
Percentage of fuel currently subject to deferred fuel accounting							85.00%
Margin deposit assets							$ 1,000,000
Margin liabilities							0		0
Capitalized interest costs and Capitalized interest costs and AFUDC							60,000,000		34,000,000		56,000,000
AFUDC recorded as regulatory asset							11,000,000		11,000,000		4,000,000
Impairment of assets and other charges							1,093,000,000		757,000,000
MW Capacity | MW					1,292
Number of facilities in cold reserve units retired | Facility					6
Retained earnings							7,758,000,000		7,167,000,000
Net unrealized losses in other income											24,000,000
Net unrealized losses in other income, after tax											18,000,000
Operating lease assets							185,000,000	[1]	212,000,000	[1]		$ 209,000,000
Operating lease liability							183,000,000
Tax reform, reclassification of tax benefit from AOCI to retained earnings											3,000,000
Virginia Electric and Power Company | Accounting Standards Update 2016-13 | Cumulative-effect of Changes in Accounting Principles
Significant Accounting Policies [Line Items]
Unrealized gains reclassified from AOCI to retained earnings											119,000,000
Unrealized gains reclassified from AOCI to retained earnings after-tax											73,000,000
Virginia Electric and Power Company | Change in Depreciation Rates from New Depreciation Study
Significant Accounting Policies [Line Items]
Increase (decrease) in depreciation expense							(31,000,000)				(60,000,000)
Increase (decrease) in depreciation expense, after tax							(23,000,000)				$ (44,000,000)
Virginia Electric and Power Company | Electric Generation Facilities
Significant Accounting Policies [Line Items]
Charges recorded with dismantling							54,000,000
Charges recorded with dismantling after tax							40,000,000
Virginia Electric and Power Company | Impairment of Assets and Other Charges
Significant Accounting Policies [Line Items]
Impairment of assets and other charges	$ 127,000,000	$ 751,000,000	17,000,000	$ 62,000,000	$ 346,000,000	$ 160,000,000	130,000,000
Asset impairment charges after tax	$ 94,000,000	$ 559,000,000	$ 12,000,000	$ 46,000,000	$ 257,000,000	$ 119,000,000	97,000,000
Virginia Electric and Power Company | Maximum
Significant Accounting Policies [Line Items]
Margin deposit assets									1,000,000
Virginia Electric and Power Company | Affiliated Entity
Significant Accounting Policies [Line Items]
Income tax payable							19,000,000		35,000,000
Virginia Electric and Power Company | Affiliated Entity | Federal
Significant Accounting Policies [Line Items]
Income tax payable							17,000,000		15,000,000
Virginia Electric and Power Company | Affiliated Entity | State
Significant Accounting Policies [Line Items]
Income tax payable							$ 2,000,000		20,000,000
DESC
Significant Accounting Policies [Line Items]
Percentage of fuel currently subject to deferred fuel accounting							96.00%
Dominion Energy Gas Holdings, LLC
Significant Accounting Policies [Line Items]
Inventory under LIFO method							$ 2,000,000		19,000,000
Amount exceeded on LIFO basis							$ 52,000,000		$ 60,000,000
Dominion Energy Midstream Partners, LP | Terra Nova Renewable Partners | Nonregulated Solar Projects | Call Option
Significant Accounting Policies [Line Items]
Percentage ownership in total units							67.00%
Cove Point | Brookfield
Significant Accounting Policies [Line Items]
Percentage of equity interest sold to noncontrolling interest owners							25.00%
Four Brothers and Three Cedars
Significant Accounting Policies [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired							50.00%
Four Brothers and Three Cedars | Dominion Energy Midstream Partners, LP | Terra Nova Renewable Partners | Nonregulated Solar Projects
Significant Accounting Policies [Line Items]
Percentage of equity interest sold to noncontrolling interest owners							33.00%

[1] Included in other deferred charges and other assets in the Companies’ Consolidated Balance Sheets.