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Acquisitions and Dispositions (Acquisition of Dominion Questar) (Narrative) (Details) - USD ($) |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Dec. 01, 2016 | Sep. 16, 2016 | Dec. 31, 2016 | Sep. 30, 2016 | Aug. 31, 2016 | Apr. 30, 2016 | Jul. 31, 2014 | Jun. 30, 2013 | Dec. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of short term notes |  |  |  |  |  |  |  |  |  |  | $ 1,200,000,000 | $ 600,000,000 | $ 400,000,000
Proceeds from issuance of common stock |  |  |  |  |  |  |  |  |  |  | 2,152,000,000 | 786,000,000 | 205,000,000
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Repayment of short-term notes |  |  |  |  |  |  |  |  |  |  | 1,800,000,000 | $ 400,000,000 | $ 400,000,000
Questar Pipeline, LLC | Dominion Midstream Partners, LP | Subsidiary of Common Parent | Disposal Group, Disposed of by Sale, Not Discontinued Operations |  |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Cash consideration | $ 823,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Debt financed distribution | 300,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Amount of consideration | 1,300,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Questar Pipeline, LLC | Dominion Midstream Partners, LP | Subsidiary of Common Parent | Partnership Interest | Disposal Group, Disposed of by Sale, Not Discontinued Operations |  |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Combined value of common and convertible preferred units | $ 467,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Questar Pipeline, LLC | Dominion Midstream Partners, LP | Limited Partner | Common Units | Disposal Group, Disposed of by Sale, Not Discontinued Operations |  |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of common units to be purchased |  |  | 6,656,839 |  |  |  |  |  |  |  |  |  |
Questar Fueling Company | Disposal Group, Disposed of by Sale, Not Discontinued Operations |  |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Cash consideration |  |  | $ 28,000,000 |  |  |  |  |  |  |  |  |  |
Senior Unsecured Promissory Note Payable | Questar Pipeline, LLC | Dominion Midstream Partners, LP | Limited Partner | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Promissory note |  |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of promissory note |  |  | $ 301,000,000 |  |  |  |  |  |  |  |  |  |
Private Placement Term Loan Agreement Maturing in September 2017 | Term loan agreement | Questar Pipeline, LLC | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Scenario, Forecast |  |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Repayment of short-term notes |  |  |  |  |  |  |  |  |  | $ 1,200,000,000 |  |  |
Underwritten Public Offering |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of common stock |  |  |  |  |  | $ 756,000,000 |  |  |  |  |  |  |
Capital Unit, Class A |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock |  |  |  |  | $ 1,400,000,000.0 |  | $ 1,000,000,000 | $ 550,000,000 |  |  |  |  |
Dominion Questar Corporation |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Price per share |  | $ 25.00 |  |  |  |  |  |  |  |  |  |  |
Total consideration |  | $ 4,400,000,000 |  |  |  |  |  |  |  |  |  |  |
Shares of Dominion Questar outstanding at closing |  | 175,500,000 |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of senior notes |  |  |  |  | 1,300,000,000 |  |  |  |  |  |  |  |
Contributions to fund Dominion Questar's qualified and non-qualified defined benefit pension plans |  | $ 75,000,000 |  |  |  |  |  |  |  |  |  |  |
Period after the closing date |  | 6 months |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in net income |  |  |  |  |  |  |  |  | $ 379,000,000 |  |  |  |
Increase in operating revenue |  |  |  |  |  |  |  |  |  |  | 73,000,000 |  |
Dominion Questar Corporation | Other operations and maintenance expense |  |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Transaction and transition costs incurred |  |  |  |  |  |  |  |  |  |  | 58,000,000 |  |
Dominion Questar Corporation | Interest and related charges |  |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Transaction and transition costs incurred |  |  |  |  |  |  |  |  |  |  | $ 16,000,000 |  |
Dominion Questar Corporation | Commitment for Charitable Contributions |  |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Charitable contributions, next twelve months |  | $ 1,000,000 |  |  |  |  |  |  |  |  |  |  |
Charitable contributions, second year |  | 1,000,000 |  |  |  |  |  |  |  |  |  |  |
Charitable contributions, third year |  | 1,000,000 |  |  |  |  |  |  |  |  |  |  |
Charitable contributions, fourth year |  | 1,000,000 |  |  |  |  |  |  |  |  |  |  |
Charitable contributions, fifth year |  | $ 1,000,000 |  |  |  |  |  |  |  |  |  |  |
Dominion Questar Corporation | Commitment for Charitable Contributions | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |
Other Commitment, Fiscal Year Maturity [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Period for charitable contributions |  | 5 years |  |  |  |  |  |  |  |  |  |  |
Dominion Questar Corporation | White River Hub, LLC |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage |  | 50.00% |  |  |  |  |  |  |  |  |  |  |
Dominion Questar Corporation | Term loan agreement |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of short term notes |  |  |  | $ 1,200,000,000 |  |  |  |  |  |  |  |  |
Dominion Questar Corporation | Underwritten Public Offering |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from issuance of common stock |  |  |  |  |  | $ 500,000,000 |  |  |  |  |  |  |
Dominion Questar Corporation | Capital Unit, Class A |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock |  |  |  |  | $ 1,400,000,000 |  |  |  |  |  |  |  |

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