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Significant Accounting Policies (Checks the Outstanding Accounts Payable but not yet Presented for Payment and Recorded) (Detail) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Accounts Payable [Line Items] |  |
Accounts payable for checks outstanding | $ 30 | $ 24
Virginia Electric and Power Company |  |
Accounts Payable [Line Items] |  |
Accounts payable for checks outstanding | 17 | 11
Dominion Energy Gas Holdings, LLC |  |
Accounts Payable [Line Items] |  |
Accounts payable for checks outstanding | $ 7 | $ 9

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- Definition Accounts Payable Checks Outstanding + 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 Accounts Payable [Line Items] + References No definition available. + Details
Name: | d_AccountsPayableLineItems
Namespace Prefix: | d_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | dei_LegalEntityAxis=d_VirginiaElectricAndPowerCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | dei_LegalEntityAxis=d_DominionEnergyGasHoldingsLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |