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Commitments and Contingencies (Narrative) (Detail) $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |  |
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Dec. 31, 2018 USD ($) Parties site | Aug. 31, 2018 USD ($) | Jun. 30, 2018 USD ($) | Sep. 30, 2017 | Jul. 31, 2017 | Jun. 30, 2017 | May 31, 2017 Counts | Apr. 30, 2017 Petition Station | Mar. 31, 2017 Counts | Aug. 31, 2016 T | Jul. 31, 2016 Parties | Apr. 30, 2015 Facilities | Dec. 31, 2018 USD ($) site | Jun. 30, 2018 USD ($) | Dec. 31, 2018 USD ($) Facility site Facilities Indicators gal | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Oct. 31, 2017 USD ($) | Oct. 31, 2015 PartsPerBillion | Jul. 31, 2015 Counts
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental Remediation Expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 81 |  | $ 197 |  |  |  |
ARO incurred |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20 | $ 37 |  |  |  |  |
Regulatory liability | $ 7,196 |  |  |  |  |  |  |  |  |  |  |  | $ 7,196 |  | 7,196 | 7,109 |  |  |  |  |
Virginia Electric and Power Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental Remediation Expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 81 |  | 197 |  |  |  |
ARO incurred |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 14 | 11 |  |  |  |  |
Regulatory liability | 4,946 |  |  |  |  |  |  |  |  |  |  |  | 4,946 |  | 4,946 | 4,887 |  |  |  |  |
Virginia Electric and Power Company | Future Ash Pond and Landfill Closure Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ARO incurred |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 131 |  |  | 238 | $ 386 |  |  |
Virginia Electric and Power Company | Increase In Property Plant And Equipment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ARO incurred |  |  |  |  |  |  |  |  |  |  |  |  |  | 46 |  |  | 17 |  |  |  |
Virginia Electric and Power Company | Increase in Regulatory Assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ARO incurred |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 |  |  | 24 |  |  |  |
Virginia Electric and Power Company | Other operations and maintenance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ARO incurred |  |  |  |  |  |  |  |  |  |  |  |  |  | 81 |  |  | $ 197 |  |  |  |
ARO incurred, after tax |  |  |  |  |  |  |  |  |  |  |  |  |  | 60 |  |  |  |  |  |  |
Dominion Energy Gas Holdings, LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ARO incurred |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 | 1 |  |  |  |  |
Regulatory liability | 789 |  |  |  |  |  |  |  |  |  |  |  | 789 |  | 789 | $ 790 |  |  |  |  |
FERC-regulated | Virginia Electric and Power Company | Pending Litigation [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory liability | $ 14 |  |  |  |  |  |  |  |  |  |  |  | 14 |  | $ 14 |  |  |  |  |  |
CWA | Virginia Electric and Power Company | Minimum | Chesapeake power station [Member] | Judicial Ruling |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional specific sediment, water and aquatic life monitoring period |  |  |  |  | 2 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
CWA | EPA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Compliance date |  |  |  | 2023-12 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
CWA | EPA | 2015 Effluent Limitations Guidelines Rule for Steam Electric Power Generating Category |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Compliance date |  |  |  | 2020-11 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unfavorable Regulatory Action | EPA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Significant emission rate per rear CO2 equivalent | T |  |  |  |  |  |  |  |  |  | 75,000 |  |  |  |  |  |  |  |  |  |  |
Electric generating station facilities heightened entrainment analysis per day | gal |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 125,000,000 |  |  |  |  |  |
Unfavorable Regulatory Action | MATS | EPA | Virginia Electric and Power Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of effective days to operate power station units |  |  |  |  |  | 90 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unfavorable Regulatory Action | Ozone Standards | EPA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Standard emission level prior to revision | PartsPerBillion |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.75 |
Revised emission standard level | PartsPerBillion |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.70 |
Unfavorable Regulatory Action | Ozone Standards | EPA | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated compliance costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 25 |  |
Unfavorable Regulatory Action | Ozone Standards | EPA | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated compliance costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 35 |  |
Unfavorable Regulatory Action | Regulations To Reduce Nitrogen Oxideand Volatile Organic Compounds Emissions [Member] | Pennsylvania Department Of Environmental Protection [Member] | Dominion Gas Holdings, LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated compliance costs |  |  |  |  |  |  |  |  |  |  |  |  | $ 35 |  |  |  |  |  |  |  |
Unfavorable Regulatory Action | CWA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of facilities that may be subject to final regulations | Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 13 |  |  |  |  |  |
Unfavorable Regulatory Action | CWA | Virginia Electric and Power Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of facilities that may be subject to final regulations | Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11 |  |  |  |  |  |
Number of mandatory facility-specific factors | Indicators |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 |  |  |  |  |  |
Number of optional facility-specific factors | Indicators |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6 |  |  |  |  |  |
Number of facilities subject to regulations | Facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9 |  |  |  |  |  |
Unfavorable Regulatory Action | CWA | Virginia Electric and Power Company | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric generating stations with water withdrawals per day | gal |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |  |  |  |
Unfavorable Regulatory Action | CWA | EPA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of separate petitions for reconsideration granted | Petition |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of former manufactured gas plant sites | site | 22 |  |  |  |  |  |  |  |  |  |  |  | 22 |  | 22 |  |  |  |  |  |
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | Former Gas Plant Site with Post Closure Groundwater Monitoring Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of former sites | site |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | Virginia Electric and Power Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of former manufactured gas plant sites | site | 3 |  |  |  |  |  |  |  |  |  |  |  | 3 |  | 3 |  |  |  |  |  |
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | Virginia Electric and Power Company | Former Gas Plant Site with Post Closure Groundwater Monitoring Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated compliance costs |  |  | $ 18 |  |  |  |  |  |  |  |  |  |  | $ 18 |  |  |  |  |  |  |
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | Virginia Electric and Power Company | Former Gas Plant Site with Post Closure Groundwater Monitoring Program | Other operations and maintenance |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental Remediation Expense |  |  | 16 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental Remediation Expense, net of tax |  |  | $ 12 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | SCANA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated compliance costs | $ 10 |  |  |  |  |  |  |  |  |  |  |  | $ 10 |  | $ 10 |  |  |  |  |  |
Number of sites under investigation, remediation and monitoring | site |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 |  |  |  |  |  |
Number of sites with an updated remediation work plan | site |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |
Updated remediation work plan, cost increase |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 8 |  |  |  |  |  |
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | Dominion Energy Gas Holdings, LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of former manufactured gas plant sites | site | 12 |  |  |  |  |  |  |  |  |  |  |  | 12 |  | 12 |  |  |  |  |  |
Unfavorable Regulatory Action | CCR | EPA | Facilities Subject to Coal Combustion Residual Final Rule | Environmental Protection Agency Final Rule Regulating Management of CCRs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of facilities with CCR | Facilities |  |  |  |  |  |  |  |  |  |  |  | 11 |  |  |  |  |  |  |  |  |
Unfavorable Regulatory Action | CCR | EPA | Virginia Electric and Power Company | Facilities Subject to Coal Combustion Residual Final Rule | Environmental Protection Agency Final Rule Regulating Management of CCRs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of facilities with CCR | Facilities |  |  |  |  |  |  |  |  |  |  |  | 8 |  |  |  |  |  |  |  |  |
Number of stations | Station |  |  |  |  |  |  |  | 4 |  |  |  |  |  |  |  |  |  |  |  |  |
Breach of Contract Lawsuit | DETI | Pending Litigation [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total number of counts in complaint | Counts |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8
Breach of Contract Lawsuit | DETI | Judicial Ruling |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of counts dismissed | Counts |  |  |  |  |  |  |  |  | 3 |  |  |  |  |  |  |  |  |  |  |  |
Breach of Contract Lawsuit | DETI | Settled Litigation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of claims withdrew | Counts |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |
payment of litigation Settlement agreement |  | $ 14 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liquefaction Project | FERC-regulated | Cove Point | Pending Litigation [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of parties | Parties | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liquefaction Project | FERC-regulated | Cove Point | Judicial Ruling |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of parties | Parties |  |  |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |

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