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Fair Value Measurements (Assets and Liabilities that are Measured at Fair Value on a Recurring Basis) (Detail) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | $ 244 |  | $ 307
Derivative Liabilities |  | 90 |  | 284
Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 129 | [1] | 166
Derivative Liabilities |  | 23 |  | 66
Dominion Energy Gas Holdings, LLC |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 44 |  | 32
Derivative Liabilities |  | 1 |  | 8
Fair Value, Measurements, Recurring |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Total assets | [2] | 5,249 |  | 5,379
Total liabilities |  | 90 |  | 284
Fair Value, Measurements, Recurring | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Total assets |  | 2,392 |  | 2,466
Total liabilities |  | 23 |  | 66
Fair Value, Measurements, Recurring | Dominion Energy Gas Holdings, LLC |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Total assets |  | 44 |  | 32
Total liabilities |  | 1 |  | 8
Fair Value, Measurements, Recurring | Equity securities: | U.S. |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [2] | 3,435 |  | 3,493
Fair Value, Measurements, Recurring | Equity securities: | U.S. | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [3] | 1,539 |  | 1,566
Fair Value, Measurements, Recurring | Fixed Income Securities | Corporate debt instruments |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [2] | 445 |  | 444
Fair Value, Measurements, Recurring | Fixed Income Securities | Corporate debt instruments | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [3] | 221 |  | 224
Fair Value, Measurements, Recurring | Fixed Income Securities | Government securities |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [2] | 1,113 |  | 1,101
Fair Value, Measurements, Recurring | Fixed Income Securities | Government securities | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [3] | 500 |  | 494
Fair Value, Measurements, Recurring | Cash equivalents and other |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [2] | 12 |  | 34
Fair Value, Measurements, Recurring | Cash equivalents and other | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [3] | 3 |  | 16
Fair Value, Measurements, Recurring | Commodity |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 156 |  | 258
Derivative Liabilities |  | 31 |  | 197
Fair Value, Measurements, Recurring | Commodity | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 123 |  | 166
Derivative Liabilities |  | 9 |  | 9
Fair Value, Measurements, Recurring | Commodity | Dominion Energy Gas Holdings, LLC |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Liabilities |  |  |  | 6
Fair Value, Measurements, Recurring | Interest rate |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 44 |  | 17
Derivative Liabilities |  | 58 |  | 85
Fair Value, Measurements, Recurring | Interest rate | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 6 |  |
Derivative Liabilities |  | 14 |  | 57
Fair Value, Measurements, Recurring | Foreign currency |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 44 |  | 32
Derivative Liabilities |  | 1 |  | 2
Fair Value, Measurements, Recurring | Foreign currency | Dominion Energy Gas Holdings, LLC |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 44 |  | 32
Derivative Liabilities |  | 1 |  | 2
Fair Value, Measurements, Recurring | Level 1 |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Total assets | [2] | 3,749 |  | 3,834
Fair Value, Measurements, Recurring | Level 1 | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Total assets |  | 1,715 |  | 1,750
Fair Value, Measurements, Recurring | Level 1 | Equity securities: | U.S. |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [2] | 3,435 |  | 3,493
Fair Value, Measurements, Recurring | Level 1 | Equity securities: | U.S. | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [3] | 1,539 |  | 1,566
Fair Value, Measurements, Recurring | Level 1 | Fixed Income Securities | Government securities |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [2] | 302 |  | 307
Fair Value, Measurements, Recurring | Level 1 | Fixed Income Securities | Government securities | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [3] | 173 |  | 168
Fair Value, Measurements, Recurring | Level 1 | Cash equivalents and other |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [2] | 12 |  | 34
Fair Value, Measurements, Recurring | Level 1 | Cash equivalents and other | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [3] | 3 |  | 16
Fair Value, Measurements, Recurring | Level 2 |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Total assets | [2] | 1,378 |  | 1,388
Total liabilities |  | 88 |  | 277
Fair Value, Measurements, Recurring | Level 2 | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Total assets |  | 558 |  | 564
Total liabilities |  | 21 |  | 61
Fair Value, Measurements, Recurring | Level 2 | Dominion Energy Gas Holdings, LLC |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Total assets |  | 44 |  | 32
Total liabilities |  | 1 |  | 6
Fair Value, Measurements, Recurring | Level 2 | Fixed Income Securities | Corporate debt instruments |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [2] | 445 |  | 444
Fair Value, Measurements, Recurring | Level 2 | Fixed Income Securities | Corporate debt instruments | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [3] | 221 |  | 224
Fair Value, Measurements, Recurring | Level 2 | Fixed Income Securities | Government securities |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [2] | 811 |  | 794
Fair Value, Measurements, Recurring | Level 2 | Fixed Income Securities | Government securities | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Investments | [3] | 327 |  | 326
Fair Value, Measurements, Recurring | Level 2 | Commodity |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 34 |  | 101
Derivative Liabilities |  | 29 |  | 190
Fair Value, Measurements, Recurring | Level 2 | Commodity | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 4 |  | 14
Derivative Liabilities |  | 7 |  | 4
Fair Value, Measurements, Recurring | Level 2 | Commodity | Dominion Energy Gas Holdings, LLC |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Liabilities |  |  |  | 4
Fair Value, Measurements, Recurring | Level 2 | Interest rate |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 44 |  | 17
Derivative Liabilities |  | 58 |  | 85
Fair Value, Measurements, Recurring | Level 2 | Interest rate | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 6 |  |
Derivative Liabilities |  | 14 |  | 57
Fair Value, Measurements, Recurring | Level 2 | Foreign currency |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 44 |  | 32
Derivative Liabilities |  | 1 |  | 2
Fair Value, Measurements, Recurring | Level 2 | Foreign currency | Dominion Energy Gas Holdings, LLC |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 44 |  | 32
Derivative Liabilities |  | 1 |  | 2
Fair Value, Measurements, Recurring | Level 3 |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 122 |  |
Total assets | [2] | 122 |  | 157
Derivative Liabilities |  | 2 |  |
Total liabilities |  | 2 |  | 7
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 119 |  |
Total assets |  | 119 |  | 152
Derivative Liabilities |  | 2 |  |
Total liabilities |  | 2 |  | 5
Fair Value, Measurements, Recurring | Level 3 | Dominion Energy Gas Holdings, LLC |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Total liabilities |  |  |  | 2
Fair Value, Measurements, Recurring | Level 3 | Commodity |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 122 |  | 157
Derivative Liabilities |  | 2 |  | 7
Fair Value, Measurements, Recurring | Level 3 | Commodity | Virginia Electric and Power Company |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Asset |  | 119 |  | 152
Derivative Liabilities |  | $ 2 |  | 5
Fair Value, Measurements, Recurring | Level 3 | Commodity | Dominion Energy Gas Holdings, LLC |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |
Derivative Liabilities |  |  |  | $ 2
[1] | Noncurrent derivative assets are presented in other deferred charges and other assets in Virginia Power's Consolidated Balance Sheets.
[2] | Includes investments held in the nuclear decommissioning and rabbi trusts. Excludes $195 million and $88 million of assets at March 31, 2018 and December 31, 2017, respectively, measured at fair value using NAV (or its equivalent) as a practical expedient which are not required to be categorized in the fair value hierarchy.
[3] | Includes investments held in the nuclear decommissioning trusts. Excludes $135 million and $27 million of assets at March 31, 2018 and December 31, 2017, respectively, measured at fair value using NAV (or its equivalent) as a practical expedient which are not required to be categorized in the fair value hierarchy.

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