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Employee Benefit Plans (Components of AOCI and Regulatory Assets and Liabilities) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items] |  |
Net actuarial loss |  | $ (25)
Dominion Gas Holdings, LLC |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net actuarial loss |  | $ (3)
Pension Benefits |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net actuarial loss | $ 161 |
Prior service (credit) cost | 1 |
Pension Benefits | Dominion Gas Holdings, LLC |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net actuarial loss | 16 |
Prior service (credit) cost | 0 |
Other Postretirement Plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net actuarial loss | 13 |
Prior service (credit) cost | (47) |
Other Postretirement Plans | Dominion Gas Holdings, LLC |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Net actuarial loss | 2 |
Prior service (credit) cost | $ 1 |

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