Regulatory Matters (Narrative) (Detail) $ in Millions			1 Months Ended							3 Months Ended		9 Months Ended	12 Months Ended
		Feb. 01, 2020	Oct. 31, 2018 USD ($) program MMcf	Sep. 30, 2018 USD ($) kV mi	Aug. 31, 2018 USD ($) project MW kV mi	Jul. 31, 2018 USD ($)	May 31, 2018 USD ($)	Aug. 31, 2009 kV	Apr. 30, 2007 kV	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Jan. 31, 2020	Dec. 31, 2017 USD ($)
Public Utilities General Disclosures [Line Items]
Regulatory assets-noncurrent				$ 2,316								$ 2,316		$ 2,480	[1]
Regulatory asset recovered through retail rates
Public Utilities General Disclosures [Line Items]
Regulatory assets-noncurrent	[2]			265								265		222
Virginia Regulation | Operating Segments
Public Utilities General Disclosures [Line Items]
Charge associated with legislation												215
Charge associated with legislation, after tax												160
Virginia Electric and Power Company
Public Utilities General Disclosures [Line Items]
Regulatory assets-noncurrent				636								636		810	[3]
Tax reform benefit					$ 100
Virginia Electric and Power Company | Subsequent Event
Public Utilities General Disclosures [Line Items]
Reduction in regulatory liabilities			$ 14
Regulatory liabilities one time bill credit amount			13
Virginia Electric and Power Company | Regulatory asset recovered through retail rates
Public Utilities General Disclosures [Line Items]
Regulatory assets-noncurrent	[2]			265								$ 265		$ 222
Virginia Electric and Power Company | Virginia Regulation
Public Utilities General Disclosures [Line Items]
Interim rate reduction amount						$ 125
Estimated recovery of fuel expenses							$ 1,500
Increase in fuel revenue					$ 209		222
Earnings above authorized return on equity (basis points)												70.00%
One-time bill credit, provisions for current customers												$ 200
Charge associated with legislation												215
Charge associated with legislation, after tax												160
Legislation amount credited in customer bill												138
Virginia Electric and Power Company | Virginia Regulation | Coastal Virginia Offshore Wind Project
Public Utilities General Disclosures [Line Items]
Capacity of wind turbine generators (mV) | MW					6
Public utilities length of wind project | mi					27
Total estimated cost of project					$ 300
Number of wind projects | project					2
Virginia Electric and Power Company | Virginia Regulation | Transmission Line Between Lanexa and Dunnsville Substations
Public Utilities General Disclosures [Line Items]
Total estimated cost of project					$ 15
Capacity of transmission line (kV) | kV					138
Virginia Electric and Power Company | Virginia Regulation | Transmission Line Between Dooms Substation and Valley Substation
Public Utilities General Disclosures [Line Items]
Total estimated cost of project				$ 65								65
Capacity of transmission line (kV) | kV				500
Length of kV line (miles) | mi				18
Virginia Electric and Power Company | Virginia Regulation | Transmission Line Between Idylwood and Tysons Substations
Public Utilities General Disclosures [Line Items]
Total estimated cost of project				$ 125								125
Capacity of transmission line (kV) | kV				230
Length of kV line (miles) | mi				4
Virginia Electric and Power Company | Virginia Regulation | Operating Segments
Public Utilities General Disclosures [Line Items]
Charge associated with legislation												215
Charge associated with legislation, after tax												160
Proposed revenue requirement					$ 636		755
Virginia Electric and Power Company | Virginia Regulation | Operating Segments | Transmission Component of Virginia Power's
Public Utilities General Disclosures [Line Items]
Proposed revenue requirement							468
Virginia Electric and Power Company | Virginia Regulation | Subsequent Event
Public Utilities General Disclosures [Line Items]
Proposed annual revenue reduction amount			151
Estimated annual revenue reduction on one-time bill credit			$ 95
Virginia Electric and Power Company | Virginia Regulation | Riders C1A and C2A | Subsequent Event | Operating Segments | Energy Efficiency Program
Public Utilities General Disclosures [Line Items]
Number of new energy efficiency programs | program			10
Period for cost cap			5 years
Number of new demand response programs | program			1
Amount of cost recovery			$ 262
Proposed revenue requirement			49
Increase (decrease) in revenue requirement			18
Virginia Electric and Power Company | Virginia Regulation | Rider BW | Subsequent Event | Operating Segments
Public Utilities General Disclosures [Line Items]
Proposed revenue requirement			123
Increase (decrease) in revenue requirement			7
Virginia Electric and Power Company | Virginia Regulation | Rider US-2 | Subsequent Event | Operating Segments
Public Utilities General Disclosures [Line Items]
Proposed revenue requirement			16
Increase (decrease) in revenue requirement			3
Virginia Electric and Power Company | Virginia Regulation | Rider T1 | Operating Segments
Public Utilities General Disclosures [Line Items]
Proposed revenue requirement					630		287
Increase (decrease) in revenue requirement							146
Virginia Electric and Power Company | North Carolina Regulation
Public Utilities General Disclosures [Line Items]
Proposed cost increase (decrease) amount					$ 24
Virginia Electric and Power Company | North Carolina Regulation | Scenario, Forecast
Public Utilities General Disclosures [Line Items]
Mitigation recoverable percentage													50.00%
Mitigation recoverable remaining percentage		50.00%
Virginia Electric and Power Company | Settled Litigation | Federal Energy Regulatory Commission | Order Regarding Transmission Rate Design For Allocation Of Costs Among P J M Interconnect L L C Transmission Customers | Unfavorable Regulatory Action
Public Utilities General Disclosures [Line Items]
Duration of payment under settlement agreement					10 years
Amount required to pay under settlement agreement					$ 276
Virginia Electric and Power Company | Settled Litigation | Federal Energy Regulatory Commission | Order Regarding Transmission Rate Design For Allocation Of Costs Among P J M Interconnect L L C Transmission Customers | Unfavorable Regulatory Action | Other Current Liabilities
Public Utilities General Disclosures [Line Items]
Amount of contingent liability				$ 170								170
Virginia Electric and Power Company | Settled Litigation | Federal Energy Regulatory Commission | Order Regarding Transmission Rate Design For Allocation Of Costs Among P J M Interconnect L L C Transmission Customers | Unfavorable Regulatory Action | Other Deferred Credits and Other Liabilities
Public Utilities General Disclosures [Line Items]
Amount of contingent liability				72								$ 72
Virginia Electric and Power Company | Settled Litigation | Federal Energy Regulatory Commission | Order Regarding Transmission Rate Design For Allocation Of Costs Among P J M Interconnect L L C Transmission Customers | Unfavorable Regulatory Action | Regulatory asset recovered through retail rates
Public Utilities General Disclosures [Line Items]
Regulatory assets-noncurrent					$ 265
Virginia Electric and Power Company | Minimum
Public Utilities General Disclosures [Line Items]
Facility operating capacity (kV) | kV									500
Virginia Electric and Power Company | Minimum | Judicial Ruling [Member]
Public Utilities General Disclosures [Line Items]
Facility operating capacity (kV) | kV								500
DETI | Federal Energy Regulatory Commission | Other operations and maintenance | Preliminary recommendation one
Public Utilities General Disclosures [Line Items]
Audit compliance charge recognized in connection with preliminary recommendation											$ 15
Audit compliance after-tax charge recognized in connection with preliminary recommendation											$ 9
DETI | Federal Energy Regulatory Commission | Other operations and maintenance | Other preliminary recommendation
Public Utilities General Disclosures [Line Items]
Audit compliance charge recognized in connection with preliminary recommendation										$ 129
Audit compliance after-tax charge recognized in connection with preliminary recommendation										$ 94
Questar Gas | Cost-of-service impact of 2017 Tax Reform Act
Public Utilities General Disclosures [Line Items]
Reduction in regulatory liabilities							$ 15
Corporate income tax reduction to customer						$ 9
Regulatory liability, amortization period							1 year
Questar Gas | Utah and Wyoming Regulation | Subsequent Event
Public Utilities General Disclosures [Line Items]
Proposed cost increase (decrease) amount			$ 48
LNG peaking storage facility, liquefaction rate per day | MMcf			8.2
East Ohio | Ohio Regulation | UEX Rider
Public Utilities General Disclosures [Line Items]
Elimination of over-recovered balance of accumulated bad debt expense				11
Prospective bad debt expense recovered				$ 16

[1] Dominion Energy’s Consolidated Balance Sheet at December 31, 2017 has been derived from the audited Consolidated Balance Sheet at that date.

[2] Reflects amounts related to the PJM transmission cost allocation matter. See Note 13 for more information.

[3] Virginia Power’s Consolidated Balance Sheet at December 31, 2017 has been derived from the audited Consolidated Balance Sheet at that date.