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Related-Party Transactions (Narrative) (Detail) - USD ($) shares in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Related Party Transaction [Line Items] |  |  |
Derivative Asset | $ 307,000,000 | $ 279,000,000 |
Derivative Liabilities | 284,000,000 | 155,000,000 |
Dominion Energy Gas Holdings, LLC |  |  |
Related Party Transaction [Line Items] |  |  |
Derivative Asset | 32,000,000 |  |
Derivative Liabilities | 8,000,000 | 11,000,000 |
Short term demand note | 18,000,000 | 118,000,000 |
Dominion Energy Gas Holdings, LLC | Revolving Credit Facility | IRCA |  |  |
Related Party Transaction [Line Items] |  |  |
Short term demand note | $ 18,000,000 | $ 118,000,000 |
Weighted- average interest rate percentage | 1.60% | 1.08% |
Dominion Energy Gas Holdings, LLC | Pension Benefits | Amounts Associated with the Dominion Pension Plan |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts due from Dominion, noncurrent | $ 734,000,000 | $ 697,000,000 |
Dominion Energy Gas Holdings, LLC | Medical Coverage for Local retirees | Amounts Associated with the Dominion Retiree Health and Welfare Plan |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts due from Dominion, noncurrent | 7,000,000 | 2,000,000 |
Virginia Electric and Power Company |  |  |
Related Party Transaction [Line Items] |  |  |
Derivative Asset | 166,000,000 | 194,000,000 |
Derivative Liabilities | 66,000,000 | 31,000,000 |
Short term demand note | 33,000,000 | 262,000,000 |
Outstanding borrowings, net of repayments, under money pool for non-regulated subsidiaries | $ 0 | $ 0 |
Issuance of common stock (in shares) | 0 | 0 | 0
Virginia Electric and Power Company | Affiliated Entity |  |  |
Related Party Transaction [Line Items] |  |  |
Derivative Asset | $ 11,000,000 | $ 41,000,000 |
Derivative Liabilities | 5,000,000 | 8,000,000 |
Virginia Electric and Power Company | Principal Owner |  |  |
Related Party Transaction [Line Items] |  |  |
Short term demand note | $ 33,000,000 | $ 262,000,000 |
Weighted- average interest rate percentage | 1.65% | 0.97% |
Virginia Electric and Power Company | Pension Benefits | Amounts Associated with the Dominion Pension Plan |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts due to Dominion, noncurrent | $ 505,000,000 | $ 396,000,000 |
Virginia Electric and Power Company | Medical Coverage for Local retirees | Amounts Associated with the Dominion Retiree Health and Welfare Plan |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts due from Dominion, noncurrent | $ 199,000,000 | $ 130,000,000 |

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