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Capacity of facility of company owned solar distribution generation facilities.

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Costs incurred asset retirement obligation incurred after tax.

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Increase Decrease In Earnings Per Share

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Number of facilities in cold reserve units retired.

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[Line Items] for Significant Accounting Policies [Table]

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Utilities operating expense, increase (decrease) in depreciation and amortization.

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Utilities operating expense, increase (decrease) in depreciation and amortization, after tax.

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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Amount of asset retirement obligations (ARO) costs incurred (whether capitalized or charged to expense) during the period.

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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Significant Accounting Policies (Narrative) (Detail) $ / shares in Units, $ in Millions	1 Months Ended					3 Months Ended			9 Months Ended		12 Months Ended
	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	May 31, 2019 USD ($)	Mar. 31, 2019 USD ($) Facility MW	Jan. 31, 2019 USD ($)	Sep. 30, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) $ / shares	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($) $ / shares
Significant Accounting Policies [Line Items]
Impairment of assets and other charges						$ 1,151		$ 85	$ 1,963	$ 1,219
Increase to nuclear decommissioning asset retirement obligation							$ 89
Change In Depreciation Rates From New Depreciation Study
Significant Accounting Policies [Line Items]
Increase in EPS \| $ / shares						$ 0.01			$ 0.02
Change In Depreciation Rates From New Depreciation Study \| Merchant generation assets \| Scenario Forecast
Significant Accounting Policies [Line Items]
Increase in EPS \| $ / shares											$ 0.03
Impairment of Assets and Other Charges
Significant Accounting Policies [Line Items]
Impairment of assets and other charges		$ 26
Asset impairment charges after tax		19
Virginia Electric and Power Company
Significant Accounting Policies [Line Items]
Impairment of assets and other charges						$ 200		$ 38	$ 1,008	$ 781
MW Capacity \| MW				1,292
Number of facilities in cold reserve units retired \| Facility				6
Virginia Electric and Power Company \| Change In Depreciation Rates From New Depreciation Study
Significant Accounting Policies [Line Items]
Increase (decrease) in depreciation expense						(8)			(24)
Increase (decrease) in depreciation expense, after tax						$ (6)			$ (18)
Virginia Electric and Power Company \| Change In Depreciation Rates From New Depreciation Study \| Merchant generation assets \| Scenario Forecast
Significant Accounting Policies [Line Items]
Increase (decrease) in depreciation expense											$ (31)
Increase (decrease) in depreciation expense, after tax											$ (23)
Virginia Electric and Power Company \| Electric Generation Facilities
Significant Accounting Policies [Line Items]
Charges recorded with dismantling							30
Charges recorded with dismantling after tax							$ 22
Virginia Electric and Power Company \| Impairment of Assets and Other Charges
Significant Accounting Policies [Line Items]
Impairment of assets and other charges	$ 754	17	$ 62	$ 369	$ 160
Asset impairment charges after tax	$ 561	$ 12	$ 46	$ 275	$ 119
Dominion Energy Midstream Partners, LP \| Terra Nova Renewable Partners \| Merchant Solar Projects \| Call Option
Significant Accounting Policies [Line Items]
Percentage ownership in total units						67.00%			67.00%
Cove Point \| Brookfield
Significant Accounting Policies [Line Items]
Percentage of equity interest sold to noncontrolling interest owners						25.00%			25.00%
Four Brothers and Three Cedars
Significant Accounting Policies [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired						50.00%			50.00%
Four Brothers and Three Cedars \| Dominion Energy Midstream Partners, LP \| Terra Nova Renewable Partners \| Merchant Solar Projects
Significant Accounting Policies [Line Items]
Percentage of equity interest sold to noncontrolling interest owners						33.00%			33.00%