Commitments and Contingencies (Narrative) (Details)	1 Months Ended													9 Months Ended	12 Months Ended
	Apr. 30, 2017	Jul. 31, 2016 party	Jun. 30, 2016 party	Apr. 30, 2016 USD ($)	Oct. 31, 2015	Jun. 30, 2015 party	Apr. 30, 2015 facility	Dec. 31, 2014 USD ($)	Oct. 31, 2014 facility	Jun. 30, 2014 unit	Jul. 31, 2013 unit	Sep. 30, 2011 party	Jul. 31, 2011 state group MW	Sep. 30, 2016 USD ($) facility party site	Dec. 31, 2015 USD ($) party
CWA | Virginia Electric and Power Company | Possum Point Power Station | Other operations and maintenance
Loss Contingencies [Line Items]
Charge as a result of settlement offer								$ 121,000,000
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 | Scenario, Forecast
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 | CAIR | EPA
Loss Contingencies [Line Items]
Number of states under EPA replacement rule | state													28
Number of groups of affected states | group													2
Unfavorable Regulatory Action | CAIR | EPA | Minimum
Loss Contingencies [Line Items]
Emissions of fossil fuel fired electric generating units (MW) | MW													25
Unfavorable Regulatory Action | Regulations to Reduce Nitrogen Oxide and Volatile Organic Compounds Emissions | Pennsylvania Department of Environmental Protection | Dominion Gas Holdings, LLC
Loss Contingencies [Line Items]
Estimated compliance costs				$ 25,000,000
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
Unfavorable Regulatory Action | CERCLA | EPA
Loss Contingencies [Line Items]
Number of parties issued UAO | party												22
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 | Dominion Gas Holdings, LLC
Loss Contingencies [Line Items]
Number of former manufactured gas plant sites | site														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
Preliminary costs for options under evaluation for site, minimum														$ 1,000,000
Preliminary costs for options under evaluation for site, maximum														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
Obligations incurred during the period															$ 386,000,000
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 | Other operations and maintenance
Loss Contingencies [Line Items]
Incremental charge upon recognition of ARO															99,000,000
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 | ARO's
Loss Contingencies [Line Items]
Increase in property plant and equipment associated with asset retirement costs															166,000,000
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 | Noncurrent Liabilities
Loss Contingencies [Line Items]
Reduction in other current liabilities															$ 121,000,000
Unfavorable Regulatory Action | CCR | EPA | Virginia Electric and Power Company | Pending Litigation | Environmental Protection Agency Final Rule Regulating Management of CCRs | Facilities Subject to CCR Final Rule | Administrative Appeals in Circuit Court for the City of Richmond
Loss Contingencies [Line Items]
Number of parties | party															2
Unfavorable Regulatory Action | CCR | EPA | Virginia Electric and Power Company | Settled Litigation | Environmental Protection Agency Final Rule Regulating Management of CCRs | Facilities Subject to CCR Final Rule | Administrative Appeals in Circuit Court for the City of Richmond
Loss Contingencies [Line Items]
Number of parties | party			1
Breach of Contract Lawsuit | DTI | Pending Litigation
Loss Contingencies [Line Items]
Accrued liability for legal matter														$ 6,000,000
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