Acquisitions and Dispositions (Narrative) (Details) $ / shares in Units, $ in Millions			1 Months Ended									3 Months Ended		12 Months Ended				18 Months Ended
		Apr. 01, 2015 USD ($) $ / shares shares	Jan. 31, 2017 USD ($) MW	Sep. 30, 2016 MW	Aug. 31, 2016 USD ($) project MW	May 31, 2016 USD ($)	Dec. 31, 2015 USD ($) project MW	Sep. 30, 2015 USD ($) project mi MW shares	Jun. 30, 2015 USD ($) project MW	Jan. 31, 2015 USD ($) mi	Mar. 31, 2014 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) project MW	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($)	Nov. 30, 2016	Jan. 31, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Project Cost															$ 40	$ 418	$ 206
Contributions from SunEdison to Four Brothers and Three Cedars															189	103
Goodwill	[1]						$ 3,294								$ 6,399	3,294	3,044	$ 6,399
Iroquois
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage	[2]														50.00%			50.00%
Merchant Solar Projects | Terra Nova Renewable Partners | Call Option
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Remaining ownership interest percentage															67.00%			67.00%
Merchant Solar Projects | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
MW Capacity | MW								425
SunEdison's ownership percentage interest in merchant solar projects								33.00%							33.00%			33.00%
Number of currently wholly-owned merchant solar projects | project								24
Number of solar projects sold under agreement | project							15
Sales price							$ 184									184				$ 117
Electric Retail Energy Marketing Business | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash consideration											$ 187
Gain on sale											100
After-tax gain on sale											57
Asset disposition adjustment											$ 31
Partnership Interest | National Grid | Iroquois
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest percentage								20.40%
Partnership Interest | NJNR Pipeline Company | Iroquois
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest percentage								5.53%
Affiliated Entity | DCG | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Dominion Midstream Partners, LP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales price		$ 501
Ownership interest percentage		100.00%
Affiliated Entity | DCG | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Dominion Midstream Partners, LP | Unsecured Promissory Note Receivable | Notes Receivable
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Term of senior unsecured promissory note payable		2 years
Senior unsecured promissory note payable by Dominion Midstream		$ 301
Interest rate (percentage)		0.60%
Affiliated Entity | Partnership Interest | DCG | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Dominion Midstream Partners, LP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of common units issued | shares		5,112,139
Value of common units at closing		$ 200
Number of trading days		10 days
Price per unit | $ / shares		$ 39.12
Dominion Midstream Partners, LP | Iroquois
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage	[2]														25.93%			25.93%
Dominion Midstream Partners, LP | Partnership Interest | Iroquois
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
SunEdison's ownership percentage interest in merchant solar projects															25.93%			25.93%
Ownership percentage								25.93%
Length of FERC regulated interstate natural gas pipeline (in miles) (nearly 1,500 miles) | mi								416
Number of common units issued | shares								8,600,000
Value of common units at closing								$ 216
Dominion Midstream Partners, LP | Partnership Interest | National Grid | Iroquois
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of common units issued | shares								6,800,000
Dominion Midstream Partners, LP | Partnership Interest | NJNR Pipeline Company | Iroquois
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of common units issued | shares								1,800,000
Dominion Gas Holdings, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill	[1]						$ 542								$ 542	542	542	$ 542
Dominion Gas Holdings, LLC | Iroquois
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage	[2]														24.07%			24.07%
Dominion Gas Holdings, LLC | Partnership Interest | Iroquois
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership percentage															24.07%			24.07%
Value of common units at closing						$ 7
Virginia Electric and Power Company
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Project Cost															$ 7	$ 43	$ 0
Individually Insignificant Solar Projects
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of equity interests acquired															100.00%			100.00%
Number of Projects | project															7
Purchase price															$ 32
MW Capacity | MW															221
Number of projects that commenced operations | project	[3]														1
Individually Insignificant Solar Projects | Scenario, Forecast
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Project Cost														$ 425
Solar Projects from Solar Frontier Americas Holding, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of equity interests acquired					100.00%
Number of Projects | project					2
Purchase price					$ 128
MW Capacity | MW					50
Solar Projects from Solar Frontier Americas Holding, LLC | Scenario, Forecast
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Project Cost												$ 130
Solar Projects from Community Energy Solar, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of equity interests acquired				100.00%
MW Capacity | MW				100
Solar Projects from Community Energy Solar, LLC | Scenario, Forecast
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Project Cost												$ 210
Solar Projects from Cypress Creek Renewables, LLC | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of equity interests acquired			100.00%
Purchase price			$ 154
MW Capacity | MW			79
Solar Projects from Cypress Creek Renewables, LLC | Scenario, Forecast | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Project Cost													$ 160
Four Brothers Solar, LLC and Three Cedars
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Remaining ownership interest percentage															50.00%			50.00%
Four Brothers Solar, LLC and Three Cedars | Investment Credits | Federal
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of expected federal investment tax credits on projects to be claimed															99.00%			99.00%
Four Brothers Solar, LLC and Three Cedars | SunEdison
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Contributions from SunEdison to Four Brothers and Three Cedars																		$ 292
Four Brothers Solar, LLC and Three Cedars | NRG Energy, Inc
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of equity interests acquired																			50.00%
Four Brothers Solar, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of equity interests acquired									50.00%
Number of Projects | project									4
Purchase price									$ 64
Project Cost															$ 670
MW Capacity | MW									320
Acquisition price payable									$ 62
Acquisition price in cash									2
Purchase price									64
Net property plant and equipment acquired									89
Amount of noncontrolling interest									$ 25
Three Cedars
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of equity interests acquired								50.00%
Number of Projects | project								3
Purchase price								$ 43
Project Cost															450
MW Capacity | MW								210
Acquisition price payable								$ 37
Acquisition price in cash								6
Purchase price								43
Net property plant and equipment acquired								65
Amount of noncontrolling interest								$ 22
Three Cedars | Current Liabilities
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payable included in other current liabilities															$ 2			$ 2
DCG
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of equity interests acquired										100.00%
Purchase price										$ 497
Net property plant and equipment acquired										$ 277
Length of FERC regulated interstate natural gas pipeline (in miles) (nearly 1,500 miles) | mi										1,500
Goodwill										$ 250
Amount expected to be deductible for tax purposes										225
Amount of regulatory liabilities										$ 38
Morgans Corner Solar Energy, LLC | Virginia Electric and Power Company
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of equity interests acquired							100.00%									100.00%
Purchase price							$ 47
MW Capacity | MW							20
Morgans Corner Solar Energy, LLC | Virginia Electric and Power Company | Solar Development Project
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total cost of project placed into service							$ 49									$ 49
Morgans Corner Solar Energy, LLC | Virginia Electric and Power Company | Supply Agreement with US Navy
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Duration of supply agreement							10 years

[1] Goodwill amounts do not contain any accumulated impairment losses.

[2] Comprised of Dominion Midstream's interest of 25.93% and Dominion Gas' interest of 24.07%. See Note 15 for more information.

[3] One of the projects, Marin Carport, began commercial operations in 2016.