Commitments and Contingencies (Narrative) (Details)	1 Months Ended											3 Months Ended
	Apr. 30, 2017 petition station	Mar. 31, 2017 USD ($) facility site count	Jul. 31, 2016 party	Apr. 30, 2016	Oct. 31, 2015	Jun. 30, 2015 party	Apr. 30, 2015 facility	Oct. 31, 2014 facility	Jun. 30, 2014 unit	Jul. 31, 2013 count unit	Jul. 31, 2011	Mar. 31, 2017 USD ($) facility site party
CWA | Virginia Electric and Power Company | Possum Point Power Station
Loss Contingencies [Line Items]
Period for remedial plan												30 days
Unfavorable Regulatory Action | EPA | Maximum
Loss Contingencies [Line Items]
Maximum period for consideration of CO2 emissions from biomass projects											3 years
Unfavorable Regulatory Action | EPA | Virginia Electric and Power Company
Loss Contingencies [Line Items]
Number of coal fired generating units | unit										3
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 | Subsequent Event
Loss Contingencies [Line Items]
Period to be in service following receipt of all required permits	20 months
Unfavorable Regulatory Action | MATS | EPA | Maximum
Loss Contingencies [Line Items]
Extension period for MATS compliance				1 year
Unfavorable Regulatory Action | Ozone Standards | EPA | Minimum
Loss Contingencies [Line Items]
Estimated compliance costs		$ 25,000,000										$ 25,000,000
Unfavorable Regulatory Action | Ozone Standards | EPA | Maximum
Loss Contingencies [Line Items]
Estimated compliance costs		$ 35,000,000										$ 35,000,000
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
Unfavorable Regulatory Action | CWA | EPA | Subsequent Event | 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		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 | Dominion 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 | Virginia Electric and Power Company
Loss Contingencies [Line Items]
Number of former manufactured gas plant sites | site		3										3
Preliminary costs for options under evaluation for site, minimum		$ 1,000,000										$ 1,000,000
Preliminary costs for options under evaluation for site, maximum		22,000,000										22,000,000
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
Unfavorable Regulatory Action | CCR | EPA | Virginia Electric and Power Company | Subsequent Event | Environmental Protection Agency Final Rule Regulating Management of CCRs | Facilities Subject to CCR Final Rule
Loss Contingencies [Line Items]
Number of stations | station	4
Breach of Contract Lawsuit | DTI | 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 | DTI | 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