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