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Employee Benefit Plans (Fair Values of Pension and Post Retirement Plan Assets by Asset Category) (Parenthetical) (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items] |  |
Common stock | $ 365 | $ 508
Pension Benefits |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pending sales of securities and advanced subscriptions | 198 |
Pending sales of securities |  | 52
Net accrued income | 20 | 24
Pending purchases of securities | 71 | 99
Other Postretirement Benefits |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Pending sales of securities | 10 | 2
Net accrued income | 2 | 2
Pending purchases of securities | $ 2 | $ 5

X
- Definition Defined benefit plan common stock. + References No definition available. + Details
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Namespace Prefix: | d_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Defined benefit plan, net accrued income. + References No definition available. + Details
Name: | d_DefinedBenefitPlanNetAccruedIncome
Namespace Prefix: | d_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Defined benefit plan, pending purchases of securities. + References No definition available. + Details
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Namespace Prefix: | d_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Defined benefit plan pending sales of securities and advanced subscriptions. + References No definition available. + Details
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Namespace Prefix: | d_
Data Type: | xbrli:monetaryItemType
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- Definition Defined benefit plan, pending sales of securities. + References No definition available. + Details
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Namespace Prefix: | d_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |