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Employee Benefit Plans (Benefit Obligation in Excess of Plan Assets) (Details) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Pension Benefits |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Benefit obligation | $ 7,386 | $ 5,728
Fair value of plan assets | 5,340 | 4,571
Pension Benefits | Dominion Gas Holdings, LLC |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Benefit obligation | 0 | 0
Fair value of plan assets | 0 | 0
Other Postretirement Plans |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Benefit obligation | 470 | 359
Fair value of plan assets | 356 | 299
Other Postretirement Plans | Dominion Gas Holdings, LLC |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Benefit obligation | 320 | 292
Fair value of plan assets | $ 299 | $ 283

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