Acquisitions and Dispositions (Acquisition of Dominion Questar) (Narrative) (Details) $ / shares in Units, shares in Thousands, MMcf in Thousands		1 Months Ended				3 Months Ended		9 Months Ended
	Sep. 16, 2016 USD ($) mi $ / shares shares MMcf	Oct. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Aug. 31, 2016 USD ($)	Apr. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) shares	Sep. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Business Acquisition [Line Items]
Issuance of common stock								$ 2,079,000,000
Issuance of short-term notes								1,200,000,000	$ 0
Issuance of common stock								2,079,000,000	717,000,000
Contributions to fund Dominion Questar's qualified and non-qualified defined benefit pension plans								12,000,000
Other Commitment, Fiscal Year Maturity [Abstract]
Repayments of short term note								600,000,000	$ 0
Subsequent Event | Questar Pipeline | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Dominion Midstream Partners, LP | Subsidiary of Common Parent
Other Commitment, Fiscal Year Maturity [Abstract]
Debt financed distribution		$ 300,000,000
Total consideration		1,300,000,000
Subsequent Event | Questar Pipeline | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Dominion Midstream Partners, LP | Subsidiary of Common Parent | Minimum
Other Commitment, Fiscal Year Maturity [Abstract]
Cash consideration		565,000,000
Subsequent Event | Questar Pipeline | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Dominion Midstream Partners, LP | Subsidiary of Common Parent | Maximum
Other Commitment, Fiscal Year Maturity [Abstract]
Cash consideration		890,000,000
Subsequent Event | Questar Pipeline | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Dominion Midstream Partners, LP | Subsidiary of Common Parent | Partnership Interest | Minimum
Other Commitment, Fiscal Year Maturity [Abstract]
Combined value of common and convertible preferred units		400,000,000
Subsequent Event | Questar Pipeline | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Dominion Midstream Partners, LP | Subsidiary of Common Parent | Partnership Interest | Maximum
Other Commitment, Fiscal Year Maturity [Abstract]
Combined value of common and convertible preferred units		$ 725,000,000
Subsequent Event | Questar Pipeline | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Scenario, Forecast | Dominion Midstream Partners, LP | Limited Partner | Common Units
Other Commitment, Fiscal Year Maturity [Abstract]
Common units to be purchased | shares						6,657
Senior Unsecured Promissory Note Payable | Subsequent Event | Questar Pipeline | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Scenario, Forecast | Dominion Midstream Partners, LP | Limited Partner | Term loan
Other Commitment, Fiscal Year Maturity [Abstract]
Repayment of term loan						$ 301,000,000
Private Placement Term Loan Agreement Maturing in September 2017 | Term loan agreement | Subsequent Event | Questar Pipeline | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Scenario, Forecast
Other Commitment, Fiscal Year Maturity [Abstract]
Repayments of short term note						$ 1,200,000,000
Underwritten Public Offering
Business Acquisition [Line Items]
Issuance of common stock					$ 756,000,000
Series A RSNs
Business Acquisition [Line Items]
Issuance of common stock				$ 1,400,000,000.0
Dominion Questar Corporation
Business Acquisition [Line Items]
Gas storage (bcf) | MMcf	56
Price per share | $ / shares	$ 25.00
Total consideration	$ 4,400,000,000
Shares of Dominion Questar outstanding at closing | shares	175,500
August 2016 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 operating revenue							$ 23,000,000	23,000,000
Increase in net income							5,000,000	5,000,000
Dominion Questar Corporation | Other operations and maintenance
Other Commitment, Fiscal Year Maturity [Abstract]
Transaction and transition costs incurred							40,000,000	47,000,000
Dominion Questar Corporation | Interest and related charges
Other Commitment, Fiscal Year Maturity [Abstract]
Transaction and transition costs incurred							$ 13,000,000	$ 13,000,000
Dominion Questar Corporation | White River Hub, LLC
Business Acquisition [Line Items]
Percentage interest	50.00%
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 | Term loan agreement
Business Acquisition [Line Items]
Issuance of short-term notes			$ 1,200,000,000
Dominion Questar Corporation | Underwritten Public Offering
Business Acquisition [Line Items]
Issuance of common stock					$ 500,000,000
Dominion Questar Corporation | Series A RSNs
Business Acquisition [Line Items]
Issuance of common stock				$ 1,400,000,000
Dominion Questar Corporation | Gas Transmission Pipeline
Business Acquisition [Line Items]
Length of natural gas pipeline (in miles) | mi	3,400
Dominion Questar Corporation | Gas Distribution Pipeline
Business Acquisition [Line Items]
Length of natural gas pipeline (in miles) | mi	27,500