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Commitments and Contingencies - Schedule of Commitments and Obligations (Parenthetical) (Detail) (USD $)
 3 Months Ended
Mar. 31, 2015
Commitments and Contingencies [Line Items]  
Derivative portfolio guarantee $ 13,000,000pom_DerivativePortfolioGuarantee
Obligations under guarantee 52,000,000pom_ObligationsUnderGuarantees
PHI [Member]  
Commitments and Contingencies [Line Items]  
Obligations under guarantee 11,000,000pom_ObligationsUnderGuarantees
/ dei_LegalEntityAxis
= pom_PepcoHoldingsIncMember
Potomac Electric Power Co [Member]  
Commitments and Contingencies [Line Items]  
Obligations under guarantee 13,000,000pom_ObligationsUnderGuarantees
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
Delmarva Power & Light Co/De [Member]  
Commitments and Contingencies [Line Items]  
Obligations under guarantee 15,000,000pom_ObligationsUnderGuarantees
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
Atlantic City Electric Co [Member]  
Commitments and Contingencies [Line Items]  
Obligations under guarantee 13,000,000pom_ObligationsUnderGuarantees
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
Leased Equipment and Fleet Vehicles [Member]  
Commitments and Contingencies [Line Items]  
Fair value of leased equipment and vehicles $ 0pom_LeaseObligationsFairValue
/ us-gaap_GuaranteeObligationsByNatureAxis
= pom_LeasedEquipmentAndFleetVehiclesMember
Minimum [Member]  
Commitments and Contingencies [Line Items]  
Lease term range 1 to 4 years
Maximum [Member]  
Commitments and Contingencies [Line Items]  
Lease term range 3 to 8 years