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Derivatives and Hedge Accounting Activities (Schedule of Derivatives not Designated as Hedging Instruments) (Detail) - Derivatives Not Designated as Hedging Instruments - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives | [1] | $ (45) | $ (63) | $ (5)
Virginia Electric and Power Company |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives | [2] | (57) | (70) | (13)
Dominion Energy Gas Holdings, LLC |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives |  |  | 1 | 6
Commodity | Operating Revenue |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives | [1] | 18 | 2 | 24
Commodity | Operating Revenue | Virginia Electric and Power Company |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives | [2],[3] | (57) | (70) | (13)
Commodity | Operating Revenue | Dominion Energy Gas Holdings, LLC |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives |  |  | 1 | 6
Commodity | Purchased Gas |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives | [1] | (3) | 4 | (14)
Commodity | Electric fuel and other energy-related purchases |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives | [1] | (59) | (70) | (14)
Commodity | Other operations and maintenance |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives | [1] | $ (1) | $ 1 |
Interest rate |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in Income on Derivatives | [1],[4] |  |  | $ (1)
[1] | Includes derivative activity amortized out of regulatory assets/liabilities. Amounts deferred into regulatory assets/liabilities have no associated effect in Dominion Energy's Consolidated Statements of Income.
[2] | Includes derivative activity amortized out of regulatory assets/liabilities. Amounts deferred into regulatory assets/liabilities have no associated effect in Virginia Power's Consolidated Statements of Income.
[3] | Amounts recorded in Virginia Power's Consolidated Statements of Income are classified in electric fuel and other energy-related purchases.
[4] | Amounts recorded in Dominion Energy's Consolidated Statements of Income are classified in interest and related charges.

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959 + Details
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