Commitments and Contingencies (Narrative) (Details) gal in Millions	1 Months Ended																		9 Months Ended
	Sep. 30, 2017 USD ($) facility petition site	Jul. 31, 2017	Jun. 30, 2017	May 31, 2017 count	Apr. 30, 2017 petition station	Mar. 31, 2017 count	Aug. 31, 2016 T	Jul. 31, 2016 party	Apr. 30, 2016	Oct. 31, 2015 ppb	Jun. 30, 2015 party	Apr. 30, 2015 facility	Oct. 31, 2014 facility gal	Jun. 30, 2014 unit	Sep. 30, 2013 Bcfe / d	Jul. 31, 2013 unit count	Dec. 31, 2011	Jul. 31, 2011	Sep. 30, 2017 USD ($) facility site party
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 | Possum Point Power Station
Loss Contingencies [Line Items]
Period for remedial plan																			30 days
CWA | Minimum | Virginia Electric and Power Company | Possum Point 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
Unfavorable Regulatory Action | EPA | Virginia Electric and Power Company
Loss Contingencies [Line Items]
Number of coal fired generating units | unit																3
Unfavorable Regulatory Action | EPA | Maximum
Loss Contingencies [Line Items]
Maximum period for consideration of CO2 emissions from biomass projects																		3 years
Unfavorable Regulatory Action | MATS | EPA
Loss Contingencies [Line Items]
Extension period for MATS compliance														1 year
Number of coal fired generating units | unit														2
Requested compliance extension under EPA Administrative Order										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 | MATS | EPA | Maximum
Loss Contingencies [Line Items]
Percentage of oil-fired units annual capacity exemption limits																	8.00%
Extension period for MATS compliance									1 year
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 | Maximum
Loss Contingencies [Line Items]
Estimated compliance costs	$ 35,000,000																		$ 35,000,000
Unfavorable Regulatory Action | Ozone Standards | EPA | Minimum
Loss Contingencies [Line Items]
Estimated compliance costs	$ 25,000,000																		$ 25,000,000
Unfavorable Regulatory Action | New Source Performance Standards
Loss Contingencies [Line Items]
Number of period court appeals DC vacated stay		90 days
Unfavorable Regulatory Action | 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													14
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																		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																		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																		3
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
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | Maximum | Virginia Electric and Power Company
Loss Contingencies [Line Items]
Estimated compliance costs	$ 22,000,000																		$ 22,000,000
Unfavorable Regulatory Action | Coal Tar and Other Potentially Harmful Materials | EPA | Minimum | Virginia Electric and Power Company
Loss Contingencies [Line Items]
Estimated compliance costs	1,000,000																		1,000,000
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
Breach of Contract Lawsuit | Dominion Energy Gas Holdings, LLC | Settled Litigation
Loss Contingencies [Line Items]
Number of claims withdrew | count				1
Breach of Contract Lawsuit | DETI | Pending Litigation
Loss Contingencies [Line Items]
Total number of counts in complaint | count																8
Accrued liability for legal matter	$ 6,000,000																		$ 6,000,000
Breach of Contract Lawsuit | DETI | Judicial Ruling
Loss Contingencies [Line Items]
Number of counts dismissed | count						3
Liquefaction Project | FERC | Cove Point | Pending Litigation
Loss Contingencies [Line Items]
Number of parties | party																			2
Liquefaction Project | FERC | Cove Point | Judicial Ruling
Loss Contingencies [Line Items]
Number of parties | party								1			1