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Commitments and Contingencies (Guarantees, Surety Bonds and Letters of Credit) (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Guarantor Obligations [Line Items]  
Exposure under guarantees $ 6,366us-gaap_GuaranteeObligationsMaximumExposure
Minimum  
Guarantor Obligations [Line Items]  
Annual future contributions 4d_AnnualFutureContributions
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum  
Guarantor Obligations [Line Items]  
Annual future contributions 19d_AnnualFutureContributions
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
Third Party and Equity Method Investee  
Guarantor Obligations [Line Items]  
Estimate of possible loss 74us-gaap_LossContingencyEstimateOfPossibleLoss
/ us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis
= d_ThirdPartyAndEquityMethodInvesteeMember
Exposure under guarantees 49us-gaap_GuaranteeObligationsMaximumExposure
/ us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis
= d_ThirdPartyAndEquityMethodInvesteeMember
Third Party and Equity Method Investee | Through 2019  
Guarantor Obligations [Line Items]  
Exposure under guarantees $ 72us-gaap_GuaranteeObligationsMaximumExposure
/ us-gaap_GuaranteeObligationsByNatureAxis
= d_Through2019Member
/ us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis
= d_ThirdPartyAndEquityMethodInvesteeMember