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Schedule I - Condensed Financial Information of Parent Company - Investment in Consolidated Companies (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Parent Company Only Financial Information [Line Items]    
Investments in Consolidated Companies $ 4,256us-gaap_EquityMethodInvestments $ 3,935us-gaap_EquityMethodInvestments
Conectiv, LLC [Member]    
Parent Company Only Financial Information [Line Items]    
Investments in Consolidated Companies 1,984us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= pom_ConectivMember		 1,730us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= pom_ConectivMember
Potomac Electric Power Co [Member]    
Parent Company Only Financial Information [Line Items]    
Investments in Consolidated Companies 2,087us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= pom_PotomacElectricPowerCoMember		 1,922us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= pom_PotomacElectricPowerCoMember
Potomac Capital Investment Corporation (PCI) [Member]    
Parent Company Only Financial Information [Line Items]    
Investments in Consolidated Companies 30us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= pom_PotomacCapitalInvestmentCorporationMember		 29us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= pom_PotomacCapitalInvestmentCorporationMember
Pepco Energy Services [Member]    
Parent Company Only Financial Information [Line Items]    
Investments in Consolidated Companies 153us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= pom_PepcoEnergyServicesMember		 250us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= pom_PepcoEnergyServicesMember
PHI Service Company [Member]    
Parent Company Only Financial Information [Line Items]    
Investments in Consolidated Companies $ 2us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= pom_PhiServiceCompanyMember		 $ 4us-gaap_EquityMethodInvestments
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= pom_PhiServiceCompanyMember