Commitments and Contingencies (Narrative) (Detail)	1 Months Ended														3 Months Ended
	Sep. 30, 2017 petition	Jul. 31, 2017	Jun. 30, 2017	May 31, 2017 count	Apr. 30, 2017 petition station	Mar. 31, 2017 count	Aug. 31, 2016 T	Jul. 31, 2016 party	Oct. 31, 2015 ppb	Jun. 30, 2015 party	Apr. 30, 2015 facility	Oct. 31, 2014 facility gal	Jun. 30, 2014	Sep. 30, 2013 Bcfe / d	Mar. 31, 2018 USD ($) facility site party	Apr. 30, 2016 USD ($)	Jul. 31, 2013 count
Ozone Standards | EPA | Maximum
Loss Contingencies [Line Items]
Maximum period to develop plans to address new standard															3 years
CWA | Virginia Electric and Power Company | Minimum | Chesapeake Power Station | 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
CCR | EPA
Loss Contingencies [Line Items]
Number of petition agreed for reconsideration | petition	2
Unfavorable Regulatory Action | Maximum | Non-FTA
Loss Contingencies [Line Items]
Authorization export approval of natural gas per day | Bcfe / d														0.77
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
Loss Contingencies [Line Items]
Requested compliance extension under EPA Administrative Order									1 year
Extension period for MATS compliance													1 year
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
Period to be in service following receipt of all required permits			23 months
Unfavorable Regulatory Action | Ozone Standards | EPA
Loss Contingencies [Line Items]
Standard emission level prior to revision | ppb									75
Revised emission standard level | ppb									70
Unfavorable Regulatory Action | Ozone Standards | EPA | Minimum
Loss Contingencies [Line Items]
Estimated compliance costs															$ 25,000,000
Unfavorable Regulatory Action | Ozone Standards | EPA | Maximum
Loss Contingencies [Line Items]
Estimated compliance costs															$ 35,000,000
Unfavorable Regulatory Action | Regulationsto Reduce Nitrogen Oxide And Volatile Organic Compounds Emissions | Pennsylvania Department Of Environmental Protection | Dominion Gas Holdings L L C
Loss Contingencies [Line Items]
Estimated compliance costs																$ 35,000,000
Unfavorable Regulatory Action | Oil And Gas New Source Performance Standards
Loss Contingencies [Line Items]
Number of period court appeals DC vacated stay		90 days
Unfavorable Regulatory Action | Oil And Gas New Source Performance Standards | EPA
Loss Contingencies [Line Items]
Requested compliance extension under EPA Administrative Order			2 years
EPA notice issued reviewing month and year															2017-04
Number of period EPA published notice of reconsideration and partial stay			90 days
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
Unfavorable Regulatory Action | CWA | EPA | Final Rule to Revise Effluent Limitations Guidelines for Steam Electric Power Generating Category
Loss Contingencies [Line Items]
Number of facilities that maybe subject to additional wastewater treatment requirements | facility															8
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															19
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
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | Virginia Electric and Power Company | Minimum
Loss Contingencies [Line Items]
Estimated compliance costs															$ 1,000,000
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | Virginia Electric and Power Company | Maximum
Loss Contingencies [Line Items]
Estimated compliance costs															$ 22,000,000
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
Unfavorable Regulatory Action | CCR | EPA | Virginia Electric and Power Company | Environmental Protection Agency Final Rule Regulating Management of CCRs | Facilities Subject to CCR Final Rule
Loss Contingencies [Line Items]
Number of facilities with CCR | facility											8
Number of stations | station					4
Unfavorable Regulatory Action | CCR | EPA | Virginia Electric and Power Company | Minimum
Loss Contingencies [Line Items]
Estimated compliance costs															$ 100,000,000
Unfavorable Regulatory Action | CCR | EPA | Virginia Electric and Power Company | Maximum
Loss Contingencies [Line Items]
Estimated compliance costs															200,000,000
Breach of Contract Lawsuit | DETI | Pending Litigation
Loss Contingencies [Line Items]
Total number of counts in complaint | count																	8
Accrued liability for legal matter															$ 7,000,000
Breach of Contract Lawsuit | DETI | Judicial Ruling
Loss Contingencies [Line Items]
Number of counts dismissed | count						3
Breach of Contract Lawsuit | DETI | Settled Litigation
Loss Contingencies [Line Items]
Number of claims withdrew | count				1
Liquefaction Project | FERC-regulated | Cove Point | Pending Litigation
Loss Contingencies [Line Items]
Number of parties | party															2
Liquefaction Project | FERC-regulated | Cove Point | Judicial Ruling
Loss Contingencies [Line Items]
Number of parties | party								1		1