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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 | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [1] | $ 148 | $ 70
Amount of Gain (Loss) Reclassified From AOCI to Income |  | (11) | 37
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [2] | 68 | 8
Virginia Electric and Power Company |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [3] | 7 |
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [4] | 68 | 8
Dominion Energy Gas Holdings, LLC |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [5] | 17 | (16)
Amount of Gain (Loss) Reclassified From AOCI to Income |  | 4 | (18)
Electric Fuel and Other Energy-Related Purchases |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified From AOCI to Income |  | 7 | (1)
Commodity |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [1] | 97 | 87
Amount of Gain (Loss) Reclassified From AOCI to Income |  | (7) | 62
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [2] | 0 | 0
Commodity | Dominion Energy Gas Holdings, LLC |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [5] | 4 | 2
Amount of Gain (Loss) Reclassified From AOCI to Income |  | (3) | (3)
Commodity | Operating Revenue |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified From AOCI to Income |  | (12) | 62
Commodity | Operating Revenue | Dominion Energy Gas Holdings, LLC |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified From AOCI to Income |  | (3) | (3)
Commodity | Purchased Gas |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Reclassified From AOCI to Income |  | (2) | 1
Interest rate |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [1],[6] | 38 | 1
Amount of Gain (Loss) Reclassified From AOCI to Income | [6] | (12) | (11)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [2],[6] | 68 | 8
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] | 7 |
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [4],[7] | 68 | 8
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] | 0 |
Amount of Gain (Loss) Reclassified From AOCI to Income | [8] | (1) | (1)
Foreign currency |  |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |  |
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) | [1],[9] | 13 | (18)
Amount of Gain (Loss) Reclassified From AOCI to Income | [9] | 8 | (14)
Increase (Decrease) in Derivatives Subject to Regulatory Treatment | [2],[9] | 0 | 0
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] | 13 | (18)
Amount of Gain (Loss) Reclassified From AOCI to Income | [10] | $ 8 | $ (14)
[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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