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Derivatives and Hedge Accounting Activities (Gains and Losses on Derivatives in Cash Flow Hedging Relationships) (Detail) - Cash Flow Hedges - 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 AOCI on Derivatives (Effective Portion) | [1] | $ 11 | $ 92 | $ 184
Amount of Gain (Loss) Reclassified From AOCI to Income |  | 47 | 259 | 176
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [2] | (58) | (26) | (9)
Virginia Electric and Power Company |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [3] | (8) | (3) | (3)
Amount of Gain (Loss) Reclassified From AOCI to Income |  | (1) | (1) | (1)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [4] | (58) | (26) | (9)
Dominion Energy Gas Holdings, LLC |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [5] | 8 | (26) | 10
Amount of Gain (Loss) Reclassified From AOCI to Income |  | 7 | (15) | 6
Commodity |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [1] | 1 | 164 | 230
Amount of Gain (Loss) Reclassified From AOCI to Income |  | 79 | 307 | 187
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [2] |  |  | 4
Commodity | Virginia Electric and Power Company |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Reclassified From AOCI to Income |  |  |  | (1)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [4] |  |  | 4
Commodity | Dominion Energy Gas Holdings, LLC |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [5] | (10) | (12) | 16
Amount of Gain (Loss) Reclassified From AOCI to Income |  | (8) | 4 | 6
Commodity | Operating Revenue |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Reclassified From AOCI to Income |  | 81 | 330 | 203
Commodity | Operating Revenue | Dominion Energy Gas Holdings, LLC |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Reclassified From AOCI to Income |  | (8) | 4 | 6
Commodity | Purchased Gas |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Reclassified From AOCI to Income |  | (2) | (13) | (15)
Commodity | Electric fuel and other energy-related purchases |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Reclassified From AOCI to Income |  |  | (10) | (1)
Commodity | Electric fuel and other energy-related purchases | Virginia Electric and Power Company |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Reclassified From AOCI to Income |  |  |  | (1)
Interest rate |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [1],[6] | (8) | (66) | (46)
Amount of Gain (Loss) Reclassified From AOCI to Income | [6] | (52) | (31) | (11)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [2],[6] | (58) | (26) | (13)
Interest rate | Virginia Electric and Power Company |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [3],[7] | (8) | (3) | (3)
Amount of Gain (Loss) Reclassified From AOCI to Income | [7] | (1) | (1) |
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [4],[7] | (58) | (26) | (13)
Interest rate | Dominion Energy Gas Holdings, LLC |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [5],[8] |  | (8) | $ (6)
Amount of Gain (Loss) Reclassified From AOCI to Income | [8] | (5) | (2) |
Foreign currency |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [1],[9] | 18 | (6) |
Amount of Gain (Loss) Reclassified From AOCI to Income | [9] | 20 | (17) |
Foreign currency | Dominion Energy Gas Holdings, LLC |  |  |  |
Derivative Instruments Gain Loss [Line Items] |  |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [5],[10] | 18 | (6) |
Amount of Gain (Loss) Reclassified From AOCI to Income | [10] | $ 20 | $ (17) |
[1] | Amounts deferred into AOCI have no associated effect in Dominion Energy's Consolidated Statements of Income.
[2] | Represents net derivative activity deferred into and amortized out of regulatory assets/liabilities. Amounts deferred into regulatory assets/liabilities have no associated effect in Dominion Energy's Consolidated Statements of Income.
[3] | Amounts deferred into AOCI have no associated effect in Virginia Power's Consolidated Statements of Income.
[4] | Represents net derivative activity deferred into and amortized out of regulatory assets/liabilities. Amounts deferred into regulatory assets/liabilities have no associated effect in Virginia Power's Consolidated Statements of Income.
[5] | Amounts deferred into AOCI have no associated effect in Dominion Energy Gas' Consolidated Statements of Income.
[6] | Amounts recorded in Dominion Energy's Consolidated Statements of Income are classified in interest and related charges.
[7] | Amounts recorded in Virginia Power's Consolidated Statements of Income are classified in interest and related charges.
[8] | Amounts recorded in Dominion Energy Gas' Consolidated Statements of Income are classified in interest and related charges.
[9] | Amounts recorded in Dominion Energy's Consolidated Statements of Income are classified in other income.
[10] | Amounts recorded in Dominion Energy Gas' Consolidated Statements of Income are classified in other income.

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