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Derivatives and Hedge Accounting Activities (Volume of Derivative Activity) (Detail) | 12 Months Ended
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Dec. 31, 2017 USD ($) MWh gal Bcf
Fixed Price - Natural Gas - Non-current Derivative Contract [Member] |  |
Derivative [Line Items] |  |
Volume of derivative activity | 19 | [1]
Fixed Price - Natural Gas - Non-current Derivative Contract [Member] | Virginia Electric and Power Company |  |
Derivative [Line Items] |  |
Volume of derivative activity | 5 | [1]
Basis - Natural Gas - Non-current Derivative Contract [Member] |  |
Derivative [Line Items] |  |
Volume of derivative activity | 600 |
Basis - Natural Gas - Non-current Derivative Contract [Member] | Virginia Electric and Power Company |  |
Derivative [Line Items] |  |
Volume of derivative activity | 540 |
Fixed Price - Electricity - Non-current Derivative Contract [Member] |  |
Derivative [Line Items] |  |
Volume of electricity | MWh | 364,990 |
Fixed Price - Electricity - Non-current Derivative Contract [Member] | Virginia Electric and Power Company |  |
Derivative [Line Items] |  |
Volume of electricity | MWh | 364,990 | [1]
Liquids - Non-current Derivative Contract [Member] |  |
Derivative [Line Items] |  |
Volume of derivative activity | gal | 10,087,200 | [2]
Liquids - Non-current Derivative Contract [Member] | Dominion Energy Gas Holdings, LLC |  |
Derivative [Line Items] |  |
Volume of derivative activity | gal | 8,491,200 |
Interest Rate - Non-current Derivative Contract |  |
Derivative [Line Items] |  |
Interest rate / Foreign currency (US Dollars, Euros) | $ | $ 4,192,517,177 | [3]
Interest Rate - Non-current Derivative Contract | Virginia Electric and Power Company |  |
Derivative [Line Items] |  |
Interest rate / Foreign currency (US Dollars, Euros) | $ | 300,000,000 | [3]
Foreign Exchange - Non- Current Derivative Contract [Member] |  |
Derivative [Line Items] |  |
Interest rate / Foreign currency (US Dollars, Euros) | $ | 280,000,000 | [3],[4]
Foreign Exchange - Non- Current Derivative Contract [Member] | Dominion Energy Gas Holdings, LLC |  |
Derivative [Line Items] |  |
Interest rate / Foreign currency (US Dollars, Euros) | $ | $ 280,000,000 | [5]
Fixed Price - Natural Gas - Current Derivative Contract |  |
Derivative [Line Items] |  |
Volume of derivative activity | 77 | [1]
Fixed Price - Natural Gas - Current Derivative Contract | Virginia Electric and Power Company |  |
Derivative [Line Items] |  |
Volume of derivative activity | 33 | [1]
Basis - Natural Gas - Current Derivative Contract |  |
Derivative [Line Items] |  |
Volume of derivative activity | 163 |
Basis - Natural Gas - Current Derivative Contract | Dominion Energy Gas Holdings, LLC |  |
Derivative [Line Items] |  |
Volume of derivative activity | 1 |
Basis - Natural Gas - Current Derivative Contract | Virginia Electric and Power Company |  |
Derivative [Line Items] |  |
Volume of derivative activity | 79 |
Fixed Price - Electricity - Current Derivative Contract |  |
Derivative [Line Items] |  |
Volume of electricity | MWh | 10,552,363 |
Fixed Price - Electricity - Current Derivative Contract | Virginia Electric and Power Company |  |
Derivative [Line Items] |  |
Volume of electricity | MWh | 1,453,910 | [1]
Financial Transmission Rights - Electricity- Current Derivative Contract |  |
Derivative [Line Items] |  |
Volume of electricity | MWh | 46,494,865 |
Liquids - Current Derivative Contract |  |
Derivative [Line Items] |  |
Volume of derivative activity | gal | 44,153,704 | [2]
Liquids - Current Derivative Contract | Dominion Energy Gas Holdings, LLC |  |
Derivative [Line Items] |  |
Volume of derivative activity | gal | 40,961,704 |
Liquids - Current Derivative Contract | Virginia Electric and Power Company |  |
Derivative [Line Items] |  |
Volume of electricity | MWh | 42,582,981 |
Interest Rate - Current Derivative Contract |  |
Derivative [Line Items] |  |
Interest rate / Foreign currency (US Dollars, Euros) | $ | $ 1,950,000,000 | [3]
Interest Rate - Current Derivative Contract | Virginia Electric and Power Company |  |
Derivative [Line Items] |  |
Interest rate / Foreign currency (US Dollars, Euros) | $ | $ 1,150,000,000 | [3]
[1] | Includes options.
[2] | Includes NGLs and oil.
[3] | Maturity is determined based on final settlement period.
[4] | Euro equivalent volumes are € 250,000,000.
[5] | Maturity is determined based on final settlement period. Euro equivalent volumes are €250,000,000.

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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