Acquisitions and Dispositions (Narrative) (Details) $ in Millions	1 Months Ended									3 Months Ended				9 Months Ended		12 Months Ended
	Oct. 31, 2017 USD ($)	Sep. 30, 2017 USD ($) project	Aug. 31, 2017 USD ($) a	Jul. 31, 2017 USD ($) a	Jul. 31, 2016 USD ($) a	Apr. 30, 2016 USD ($) a	Jan. 31, 2016 USD ($) a	Mar. 31, 2015 a	Dec. 31, 2013 USD ($) a field	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2019 USD ($) MW	Dec. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Nov. 30, 2014 a field
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cost of project														$ 343	$ 21
Virginia Electric and Power Company | Two Solar Development Projects
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of projects | project		2
Dominion Energy Gas Holdings, LLC | Marcellus Shale | Shale development rights
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Amount of consideration				$ 5	$ 5		$ 5		$ 200
Gain on sale of assets				5	5		5
After tax gain on sale of assets				$ 3	$ 3		$ 3
Development rights (number of acres) | a				2,000	2,000		2,000		79,000										24,000
Number of natural gas storage fields | field									1										1
Period for payments related to conveyance of natural gas storage fields									9 years
Dominion Energy Gas Holdings, LLC | Marcellus Shale | Shale development rights | Amended Agreement to Extend Conveyance of Development Rights
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of assets													$ 56
After tax gain on sale of assets													33
Development rights (number of acres) | a			70,000			70,000
Period for payments related to conveyance of natural gas storage fields								2 years
Development rights conveyed (number of acres) | a								9,000
Partial interest percentage conveyed						32.00%
Gas and oil area developed net remaining interest conveyed percentage			68.00%
Total consideration			$ 130
Dominion Energy Gas Holdings, LLC | Marcellus Shale | Shale development rights | Amended Agreement to Extend Conveyance of Development Rights | Other Operations And Maintenance Expense
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenue recognized						$ 35
Revenue recognized net of tax						$ 21
Scenario, Forecast | Virginia Electric and Power Company | Two Solar Development Projects
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
MW capacity | MW																155
Scenario, Forecast | Virginia Electric and Power Company | First Solar Development Project
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cost of project																	$ 140
Scenario, Forecast | Virginia Electric and Power Company | Second Solar Development Project
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cost of project																$ 140
Scenario, Forecast | Dominion Energy Gas Holdings, LLC | Marcellus Shale | Shale development rights | Amended Agreement to Extend Conveyance of Development Rights
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total consideration											$ 65	$ 65
Scenario, Forecast | Dominion Energy Gas Holdings, LLC | Marcellus Shale | Shale development rights | Amended Agreement to Extend Conveyance of Development Rights | Royalty Interest
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of assets												9
After tax gain on sale of assets												5
Scenario, Forecast | Dominion Energy Gas Holdings, LLC | Marcellus Shale | Shale development rights | Amended Agreement to Extend Conveyance of Development Rights | Final Conveyance
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of assets												65
After tax gain on sale of assets												40
Retail Energy Marketing Assets | Scenario, Forecast | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of assets										$ 65		78
After tax gain on sale of assets										$ 40		$ 48
Assignment of Tower Rental Portfolio | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Virginia Electric and Power Company
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Amount of consideration																		$ 91
Amount recognized in other income from sale													2	10
Amount to be recognized in other income ratably through 2023		$ 36											$ 36	$ 36
Subsequent Event | Retail Energy Marketing Assets | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Amount of consideration	$ 143
Contractual term of agreement to use brand	10 years