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Debt - Additional Information (Detail) (USD $)
 12 Months Ended 0 Months Ended 1 Months Ended 0 Months Ended
Dec. 31, 2014
Sublimit
Dec. 31, 2013
Apr. 15, 2014
May 10, 2013
Aug. 31, 2014
Oct. 24, 2013
Dec. 31, 2014
Mar. 31, 2014
Jun. 30, 2014
Debt Instrument [Line Items]                  
Maturities of long term debt, 2015 $ 410,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths           $ 410,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths    
Maturities of long term debt, 2016 340,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo           340,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo    
Maturities of long term debt, 2017 131,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree           131,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree    
Maturities of long term debt, 2018 285,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour           285,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour    
Maturities of long term debt, 2019 30,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive           30,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive    
Maturities of long term debt, thereafter 3,836,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive           3,836,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive    
Ongoing commercial paper 875,000,000pom_CommercialPaperProgramMaximum           875,000,000pom_CommercialPaperProgramMaximum    
Commercial paper outstanding 729,000,000us-gaap_ShortTermBorrowings 565,000,000us-gaap_ShortTermBorrowings         729,000,000us-gaap_ShortTermBorrowings    
Commercial paper weighted average maturity, in days 6 days 5 days              
Variable rate demand bonds maturing 2015 to 2017 26,000,000pom_VariableRateDemandBondsMaturityTwoThousandFifteenToTwoThousandSeventeen           26,000,000pom_VariableRateDemandBondsMaturityTwoThousandFifteenToTwoThousandSeventeen    
Variable rate demand bonds maturing 2024 33,000,000pom_VariableRateDemandBondsMaturityTwoThousandTwentyFour           33,000,000pom_VariableRateDemandBondsMaturityTwoThousandTwentyFour    
Variable rate demand bonds maturing 2028 to 2029 46,000,000pom_VariableRateDemandBondsMaturityTwoThousandTwentyEightToTwoThousandTwentyNine           46,000,000pom_VariableRateDemandBondsMaturityTwoThousandTwentyEightToTwoThousandTwentyNine    
Variable rate demand bonds weighted average interest rate 0.19%pom_VariableRateDemandBondsWeightedAverageInterestRate 0.24%pom_VariableRateDemandBondsWeightedAverageInterestRate              
Credit facility, termination date Aug. 01, 2018                
Line of credit facility maximum borrowing capacity 1,500,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity           1,500,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity    
Parent company credit facility letter of credit, maximum 500,000,000pom_ParentCompanyCreditFacilityLetterOfCreditMaximum                
Same day borrowings maximum percentage amount 10.00%pom_SameDayBorrowingsMaximumPercentageAmount                
Swingline loan repayment period 14 days                
Credit facility borrowing capacity 750,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity           750,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity    
Maximum amount of credit available to parent 1,250,000,000pom_CombinedMaximumAmountOfCreditFacilityAvailableToParent                
Subsidiary borrowing limit under parent's credit facility 500,000,000pom_SubsidiaryBorrowingLimitUnderParentsCreditFacility                
Maximum number of sublimit reallocations per year 8pom_MaximumNumberOfSublimitReallocationPerYear                
Debt instrument variable interest rate in addition to one month LIBOR's effective rate 1.00%pom_DebtInstrumentVariableInterestRateInAdditionToOneMonthLiborsEffectiveRate           1.00%pom_DebtInstrumentVariableInterestRateInAdditionToOneMonthLiborsEffectiveRate    
Borrowing capacity under the credit facility 875,000,000pom_ParentCompanyBorrowingCapacityUnderCreditFacilities 1,063,000,000pom_ParentCompanyBorrowingCapacityUnderCreditFacilities         875,000,000pom_ParentCompanyBorrowingCapacityUnderCreditFacilities    
Utility subsidiaries combined cash and borrowing capacity 413,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount 332,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount         413,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount    
Amended description of Change in Control The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.                
Ownership percentage of outstanding voting stock for Change in Control 100.00%pom_OwnershipPercentageBasisPointForChangeInControl           100.00%pom_OwnershipPercentageBasisPointForChangeInControl    
Purchase price 12,000,000pom_PurchasePriceUnderAgreementToSell                
Contract payment period 9 years                
Commercial Paper [Member]                  
Debt Instrument [Line Items]                  
Commercial paper outstanding 624,000,000us-gaap_ShortTermBorrowings
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		 442,000,000us-gaap_ShortTermBorrowings
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		         624,000,000us-gaap_ShortTermBorrowings
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		    
Commercial paper weighted average interest rate 0.57%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		 0.70%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		         0.57%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		    
Federal Funds Effective Rate [Member]                  
Debt Instrument [Line Items]                  
Debt instrument variable interest rate in addition to the federal funds effective rate 0.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_VariableRateAxis
= us-gaap_FederalFundsEffectiveSwapRateMember		                
First Mortgage Bonds [Member] | 4.65% Due 2014 [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, interest percentage 4.65%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_FourPointSixFivePercentageDueTwoThousandFourteenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		   4.65%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_FourPointSixFivePercentageDueTwoThousandFourteenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		       4.65%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_FourPointSixFivePercentageDueTwoThousandFourteenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		    
Repayment of first mortgage bonds 175,000,000us-gaap_RepaymentsOfFirstMortgageBond
/ us-gaap_DebtInstrumentAxis
= pom_FourPointSixFivePercentageDueTwoThousandFourteenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		   175,000,000us-gaap_RepaymentsOfFirstMortgageBond
/ us-gaap_DebtInstrumentAxis
= pom_FourPointSixFivePercentageDueTwoThousandFourteenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		            
First Mortgage Bonds [Member] | 3.60% Due 2024 [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, face amount 400,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointSixZeroPercentageNotesDueTwoThousandAndTwentyFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           400,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointSixZeroPercentageNotesDueTwoThousandAndTwentyFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		    
Debt instrument, maturity date Mar. 15, 2024                
Debt instrument, interest percentage 3.60%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointSixZeroPercentageNotesDueTwoThousandAndTwentyFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           3.60%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointSixZeroPercentageNotesDueTwoThousandAndTwentyFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		    
First Mortgage Bonds [Member] | 3.50% Due 2023 [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, face amount 200,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointFivePercentageDueTwoThousandTwentyThreeMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           200,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointFivePercentageDueTwoThousandTwentyThreeMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		    
Debt instrument, maturity date Nov. 15, 2023                
Debt instrument, interest percentage 3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointFivePercentageDueTwoThousandTwentyThreeMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointFivePercentageDueTwoThousandTwentyThreeMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		    
Debt instrument, premium 4,000,000us-gaap_DebtInstrumentUnamortizedPremium
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointFivePercentageDueTwoThousandTwentyThreeMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           4,000,000us-gaap_DebtInstrumentUnamortizedPremium
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointFivePercentageDueTwoThousandTwentyThreeMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		    
First Mortgage Bonds [Member] | 3.375% Due 2024 [Member]                  
Debt Instrument [Line Items]                  
Net proceeds from issuance of bonds 7,200,000us-gaap_ProceedsFromIssuanceOfDebt
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointThreeSevenFivePercentageNotesDueOnTwoThousandAndTwentyFourMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		                
First Mortgage Bonds [Member] | 7.63% Secured Medium Term Notes, Due 2014 [Member]                  
Debt Instrument [Line Items]                  
Repayment of medium term notes 7,000,000us-gaap_RepaymentsOfMediumTermNotes
/ us-gaap_DebtInstrumentAxis
= pom_SevenPointSixThreePercentageNotesDueOnTwoThousandFourteenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		                
First Mortgage Bonds [Member] | May.10, 2013 ACE Term Loan Repaid Aug. 21, 2014 [Member]                  
Debt Instrument [Line Items]                  
Prepayment of term loan 100,000,000pom_RepaymentOfTermLoanFacility
/ us-gaap_DebtInstrumentAxis
= pom_MayTenTwoThousandThirteenAceTermLoanRepaidAugustTwentyOneThousandFourteenMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		                
Maximum [Member]                  
Debt Instrument [Line Items]                  
Ratio of indebtedness to total capitalization 65.00%pom_RatioOfIndebtednessToCapitalization
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		                
Ratio of deferrable interest subordinated debt to total capitalization 15.00%pom_RatioOfDeferrableInterestSubordinatedDebtToCapitalization
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		           15.00%pom_RatioOfDeferrableInterestSubordinatedDebtToCapitalization
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		    
Delmarva Power & Light Co/De [Member]                  
Debt Instrument [Line Items]                  
Repayment of first mortgage bonds 100,000,000us-gaap_RepaymentsOfFirstMortgageBond
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		                
Maturities of long term debt, 2015 100,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           100,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Maturities of long term debt, 2016 100,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           100,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Maturities of long term debt, 2017 14,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           14,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Maturities of long term debt, 2018 4,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           4,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Maturities of long term debt, 2019 12,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           12,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Maturities of long term debt, thereafter 838,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           838,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Ongoing commercial paper 500,000,000pom_CommercialPaperProgramMaximum
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           500,000,000pom_CommercialPaperProgramMaximum
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Commercial paper outstanding 211,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		 252,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		         211,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Commercial paper weighted average maturity, in days 5 days 3 days              
Variable rate demand bonds amount 105,000,000pom_VariableRateDemandBondsAmount
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		                
Variable rate demand bonds maturing 2024 33,000,000pom_VariableRateDemandBondsMaturityTwoThousandTwentyFour
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           33,000,000pom_VariableRateDemandBondsMaturityTwoThousandTwentyFour
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Variable rate demand bonds weighted average interest rate 0.19%pom_VariableRateDemandBondsWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		 0.26%pom_VariableRateDemandBondsWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		              
Credit facility, termination date Aug. 01, 2018                
Line of credit facility maximum borrowing capacity 1,500,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           1,500,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Parent company credit facility letter of credit, maximum 500,000,000pom_ParentCompanyCreditFacilityLetterOfCreditMaximum
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		                
Same day borrowings maximum percentage amount 10.00%pom_SameDayBorrowingsMaximumPercentageAmount
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		                
Swingline loan repayment period 14 days                
Credit facility borrowing capacity 250,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           250,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Maximum amount of credit available to parent 1,250,000,000pom_CombinedMaximumAmountOfCreditFacilityAvailableToParent
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		                
Subsidiary borrowing limit under parent's credit facility 500,000,000pom_SubsidiaryBorrowingLimitUnderParentsCreditFacility
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		                
Maximum number of sublimit reallocations per year 8pom_MaximumNumberOfSublimitReallocationPerYear
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		                
Debt instrument variable interest rate in addition to one month LIBOR's effective rate 1.00%pom_DebtInstrumentVariableInterestRateInAdditionToOneMonthLiborsEffectiveRate
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           1.00%pom_DebtInstrumentVariableInterestRateInAdditionToOneMonthLiborsEffectiveRate
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Utility subsidiaries combined cash and borrowing capacity 413,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		 332,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		         413,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Amended description of Change in Control The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.                
Ownership percentage of outstanding voting stock for Change in Control 100.00%pom_OwnershipPercentageBasisPointForChangeInControl
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           100.00%pom_OwnershipPercentageBasisPointForChangeInControl
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Variable rate demand bonds maturing 2017 26,000,000pom_VariableRateDemandBondsMaturityTwoThousandSeventeen
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           26,000,000pom_VariableRateDemandBondsMaturityTwoThousandSeventeen
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Variable rate demand bonds maturing 2028 16,000,000pom_VariableRateDemandBondsMaturityTwoThousandTwentyEight
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           16,000,000pom_VariableRateDemandBondsMaturityTwoThousandTwentyEight
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Variable rate demand bonds maturing 2029 30,000,000pom_VariableRateDemandBondsMaturityTwoThousandTwentyNine
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		           30,000,000pom_VariableRateDemandBondsMaturityTwoThousandTwentyNine
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		    
Delmarva Power & Light Co/De [Member] | Commercial Paper [Member]                  
Debt Instrument [Line Items]                  
Commercial paper outstanding 106,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		 147,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		         106,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		    
Commercial paper weighted average interest rate 0.26%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		 0.29%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		         0.26%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		    
Delmarva Power & Light Co/De [Member] | Federal Funds Effective Rate [Member]                  
Debt Instrument [Line Items]                  
Debt instrument variable interest rate in addition to the federal funds effective rate 0.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_VariableRateAxis
= us-gaap_FederalFundsEffectiveSwapRateMember		                
Delmarva Power & Light Co/De [Member] | 5.00% Due 2014 [Member]                  
Debt Instrument [Line Items]                  
Repayment of unsecured notes 100,000,000us-gaap_RepaymentsOfUnsecuredDebt
/ us-gaap_DebtInstrumentAxis
= pom_FivePercentageNotesDueTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		                
Delmarva Power & Light Co/De [Member] | Medium-Term Notes [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, face amount 100,000,000us-gaap_DebtInstrumentFaceAmount
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember		           100,000,000us-gaap_DebtInstrumentFaceAmount
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember		    
Delmarva Power & Light Co/De [Member] | First Mortgage Bonds [Member]                  
Debt Instrument [Line Items]                  
Variable rate demand bonds amount 72,000,000pom_VariableRateDemandBondsAmount
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		                
Delmarva Power & Light Co/De [Member] | First Mortgage Bonds [Member] | 3.50% Due 2023 [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, face amount                 200,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointFivePercentageDueTwoThousandTwentyThreeMember
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember
Debt instrument, maturity date Nov. 15, 2023                
Debt instrument, interest percentage 3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointFivePercentageDueTwoThousandTwentyThreeMember
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointFivePercentageDueTwoThousandTwentyThreeMember
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		   3.50%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointFivePercentageDueTwoThousandTwentyThreeMember
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember
Debt instrument, premium                 4,000,000us-gaap_DebtInstrumentUnamortizedPremium
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointFivePercentageDueTwoThousandTwentyThreeMember
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember
Delmarva Power & Light Co/De [Member] | Unsecured Notes [Member] | 5.00% Due 2014 [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, interest percentage 5.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_FivePercentageNotesDueTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		           5.00%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_FivePercentageNotesDueTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		    
Repayment of first mortgage bonds 100,000,000us-gaap_RepaymentsOfFirstMortgageBond
/ us-gaap_DebtInstrumentAxis
= pom_FivePercentageNotesDueTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_UnsecuredDebtMember		                
Delmarva Power & Light Co/De [Member] | Maximum [Member]                  
Debt Instrument [Line Items]                  
Ratio of indebtedness to total capitalization 65.00%pom_RatioOfIndebtednessToCapitalization
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		                
Ratio of deferrable interest subordinated debt to total capitalization 15.00%pom_RatioOfDeferrableInterestSubordinatedDebtToCapitalization
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		           15.00%pom_RatioOfDeferrableInterestSubordinatedDebtToCapitalization
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		    
Atlantic City Electric Co [Member]                  
Debt Instrument [Line Items]                  
Maturities of long term debt, 2015 15,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		           15,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Maturities of long term debt, 2016 2,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		           2,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Maturities of long term debt, 2017 0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		           0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Maturities of long term debt, 2018 250,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		           250,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Maturities of long term debt, 2019 0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		           0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Maturities of long term debt, thereafter 637,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		           637,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Ongoing commercial paper 350,000,000pom_CommercialPaperProgramMaximum
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		           350,000,000pom_CommercialPaperProgramMaximum
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Commercial paper outstanding 127,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		 138,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		         127,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Commercial paper weighted average maturity, in days 5 days 4 days              
Variable rate demand bonds amount 18,000,000pom_VariableRateDemandBondsAmount
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		                
Variable rate demand bonds weighted average interest rate 0.05%pom_VariableRateDemandBondsWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		 0.11%pom_VariableRateDemandBondsWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		              
Credit facility, termination date Aug. 01, 2018                
Line of credit facility maximum borrowing capacity 1,500,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		           1,500,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Parent company credit facility letter of credit, maximum 500,000,000pom_ParentCompanyCreditFacilityLetterOfCreditMaximum
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		                
Same day borrowings maximum percentage amount 10.00%pom_SameDayBorrowingsMaximumPercentageAmount
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		                
Swingline loan repayment period 14 days                
Credit facility borrowing capacity 250,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		           250,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Maximum amount of credit available to parent 1,250,000,000pom_CombinedMaximumAmountOfCreditFacilityAvailableToParent
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		                
Subsidiary borrowing limit under parent's credit facility 500,000,000pom_SubsidiaryBorrowingLimitUnderParentsCreditFacility
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		                
Maximum number of sublimit reallocations per year 8pom_MaximumNumberOfSublimitReallocationPerYear
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		                
Debt instrument variable interest rate in addition to one month LIBOR's effective rate 1.00%pom_DebtInstrumentVariableInterestRateInAdditionToOneMonthLiborsEffectiveRate
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		           1.00%pom_DebtInstrumentVariableInterestRateInAdditionToOneMonthLiborsEffectiveRate
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Utility subsidiaries combined cash and borrowing capacity 413,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		 332,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		         413,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Amended description of Change in Control The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.                
Ownership percentage of outstanding voting stock for Change in Control 100.00%pom_OwnershipPercentageBasisPointForChangeInControl
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		           100.00%pom_OwnershipPercentageBasisPointForChangeInControl
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		    
Atlantic City Electric Co [Member] | Commercial Paper [Member]                  
Debt Instrument [Line Items]                  
Commercial paper outstanding 127,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		 120,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		         127,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		    
Commercial paper weighted average interest rate 0.27%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		 0.31%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		         0.27%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		    
Atlantic City Electric Co [Member] | Federal Funds Effective Rate [Member]                  
Debt Instrument [Line Items]                  
Debt instrument variable interest rate in addition to the federal funds effective rate 0.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_VariableRateAxis
= us-gaap_FederalFundsEffectiveSwapRateMember		                
Atlantic City Electric Co [Member] | Term Loan Agreement [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, face amount       100,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= pom_TermLoanAgreementMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		          
Debt instrument variable interest rate in addition to the federal funds effective rate       0.75%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_DebtInstrumentAxis
= pom_TermLoanAgreementMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember		          
Atlantic City Electric Co [Member] | Medium-Term Notes [Member] | 7.63% Secured Medium Term Notes, Due 2014 [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, interest percentage 7.63%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_SevenPointSixThreePercentageNotesDueOnTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember		           7.63%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_SevenPointSixThreePercentageNotesDueOnTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember		    
Repayment of medium term notes         7,000,000us-gaap_RepaymentsOfMediumTermNotes
/ us-gaap_DebtInstrumentAxis
= pom_SevenPointSixThreePercentageNotesDueOnTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember		        
Atlantic City Electric Co [Member] | Senior Medium Term Notes One [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, face amount 242,000,000us-gaap_DebtInstrumentFaceAmount
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_SeniorMediumTermNotesOneMember		           242,000,000us-gaap_DebtInstrumentFaceAmount
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_SeniorMediumTermNotesOneMember		    
Atlantic City Electric Co [Member] | Unsecured Tax-Exempt Bonds [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, face amount 62,000,000us-gaap_DebtInstrumentFaceAmount
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_UnsecuredTaxExemptBondsMember		           62,000,000us-gaap_DebtInstrumentFaceAmount
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_UnsecuredTaxExemptBondsMember		    
Atlantic City Electric Co [Member] | First Mortgage Bonds [Member] | 3.375% Due 2024 [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, face amount 150,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointThreeSevenFivePercentageNotesDueOnTwoThousandAndTwentyFourMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           150,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointThreeSevenFivePercentageNotesDueOnTwoThousandAndTwentyFourMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		    
Debt instrument, maturity date Sep. 01, 2024                
Debt instrument, interest percentage 3.375%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointThreeSevenFivePercentageNotesDueOnTwoThousandAndTwentyFourMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           3.375%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointThreeSevenFivePercentageNotesDueOnTwoThousandAndTwentyFourMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		    
Net proceeds from issuance of bonds 7,200,000us-gaap_ProceedsFromIssuanceOfDebt
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointThreeSevenFivePercentageNotesDueOnTwoThousandAndTwentyFourMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		                
Atlantic City Electric Co [Member] | First Mortgage Bonds [Member] | 7.63% Secured Medium Term Notes, Due 2014 [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, interest percentage 7.63%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_SevenPointSixThreePercentageNotesDueOnTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           7.63%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_SevenPointSixThreePercentageNotesDueOnTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		    
Repayment of medium term notes         7,000,000us-gaap_RepaymentsOfMediumTermNotes
/ us-gaap_DebtInstrumentAxis
= pom_SevenPointSixThreePercentageNotesDueOnTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		        
Atlantic City Electric Co [Member] | First Mortgage Bonds [Member] | May.10, 2013 ACE Term Loan Repaid Aug. 21, 2014 [Member]                  
Debt Instrument [Line Items]                  
Prepayment of term loan 100,000,000pom_RepaymentOfTermLoanFacility
/ us-gaap_DebtInstrumentAxis
= pom_MayTenTwoThousandThirteenAceTermLoanRepaidAugustTwentyOneThousandFourteenMember
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		                
Atlantic City Electric Co [Member] | Transition Bonds [Member]                  
Debt Instrument [Line Items]                  
Maturities of long term debt, 2015 44,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		           44,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		    
Maturities of long term debt, 2016 46,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		           46,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		    
Maturities of long term debt, 2017 35,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		           35,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		    
Maturities of long term debt, 2018 31,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		           31,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		    
Maturities of long term debt, 2019 18,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		           18,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		    
Maturities of long term debt, thereafter 41,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		           41,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_LongtermDebtTypeAxis
= pom_TransitionBondsMember		    
Atlantic City Electric Co [Member] | Maximum [Member]                  
Debt Instrument [Line Items]                  
Ratio of indebtedness to total capitalization 65.00%pom_RatioOfIndebtednessToCapitalization
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		                
Ratio of deferrable interest subordinated debt to total capitalization 15.00%pom_RatioOfDeferrableInterestSubordinatedDebtToCapitalization
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		           15.00%pom_RatioOfDeferrableInterestSubordinatedDebtToCapitalization
/ dei_LegalEntityAxis
= pom_AtlanticCityElectricCoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		    
Potomac Capital Investment Corporation (PCI) [Member] | Bank Loan Member]                  
Debt Instrument [Line Items]                  
Repayment of first mortgage bonds 11,000,000us-gaap_RepaymentsOfFirstMortgageBond
/ us-gaap_InvestmentTypeAxis
= us-gaap_BankLoanObligationsMember
/ dei_LegalEntityAxis
= pom_PotomacCapitalInvestmentCorporationMember		                
Pepco Energy Services [Member]                  
Debt Instrument [Line Items]                  
Maturities of long term debt, 2015 2,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		           2,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		    
Maturities of long term debt, 2016 1,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		           1,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		    
Maturities of long term debt, 2017 1,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		           1,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		    
Maturities of long term debt, 2018 1,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		           1,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		    
Maturities of long term debt, 2019 2,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		           2,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		    
Maturities of long term debt, thereafter 3,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		           3,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		    
Total long term project funding 10,000,000pom_OtherLongTermProjectDebt
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		 12,000,000pom_OtherLongTermProjectDebt
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		         10,000,000pom_OtherLongTermProjectDebt
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		    
Purchase price           7,000,000pom_PurchasePriceUnderAgreementToSell
/ dei_LegalEntityAxis
= pom_PepcoEnergyServicesMember		      
Contract payment period           23 years      
Potomac Electric Power Co [Member]                  
Debt Instrument [Line Items]                  
Maturities of long term debt, 2015 0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		           0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Maturities of long term debt, 2016 0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		           0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Maturities of long term debt, 2017 0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		           0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Maturities of long term debt, 2018 0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		           0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Maturities of long term debt, 2019 0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		           0us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Maturities of long term debt, thereafter 2,135,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		           2,135,000,000us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Ongoing commercial paper 500,000,000pom_CommercialPaperProgramMaximum
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		           500,000,000pom_CommercialPaperProgramMaximum
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Commercial paper outstanding 104,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		 151,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		         104,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Commercial paper weighted average maturity, in days 6 days 5 days              
Credit facility, termination date Aug. 01, 2018                
Line of credit facility maximum borrowing capacity 1,500,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		           1,500,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Parent company credit facility letter of credit, maximum 500,000,000pom_ParentCompanyCreditFacilityLetterOfCreditMaximum
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		                
Same day borrowings maximum percentage amount 10.00%pom_SameDayBorrowingsMaximumPercentageAmount
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		                
Swingline loan repayment period 14 days                
Credit facility borrowing capacity 250,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		           250,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Maximum amount of credit available to parent 1,250,000,000pom_CombinedMaximumAmountOfCreditFacilityAvailableToParent
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		                
Subsidiary borrowing limit under parent's credit facility 500,000,000pom_SubsidiaryBorrowingLimitUnderParentsCreditFacility
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		                
Maximum number of sublimit reallocations per year 8pom_MaximumNumberOfSublimitReallocationPerYear
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		                
Debt instrument variable interest rate in addition to one month LIBOR's effective rate 1.00%pom_DebtInstrumentVariableInterestRateInAdditionToOneMonthLiborsEffectiveRate
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		           1.00%pom_DebtInstrumentVariableInterestRateInAdditionToOneMonthLiborsEffectiveRate
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Utility subsidiaries combined cash and borrowing capacity 413,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		 332,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		         413,000,000us-gaap_DebtInstrumentUnusedBorrowingCapacityAmount
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Amended description of Change in Control The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.                
Ownership percentage of outstanding voting stock for Change in Control 100.00%pom_OwnershipPercentageBasisPointForChangeInControl
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		           100.00%pom_OwnershipPercentageBasisPointForChangeInControl
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		    
Purchase price 12,000,000pom_PurchasePriceUnderAgreementToSell
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember		                
Contract payment period             9 years    
Potomac Electric Power Co [Member] | Commercial Paper [Member]                  
Debt Instrument [Line Items]                  
Commercial paper outstanding 104,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		 151,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		         104,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		    
Commercial paper weighted average interest rate 0.28%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		 0.34%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		         0.28%us-gaap_ShortTermDebtWeightedAverageInterestRate
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		    
Potomac Electric Power Co [Member] | Federal Funds Effective Rate [Member]                  
Debt Instrument [Line Items]                  
Debt instrument variable interest rate in addition to the federal funds effective rate 0.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_VariableRateAxis
= us-gaap_FederalFundsEffectiveSwapRateMember		                
Potomac Electric Power Co [Member] | Medium-Term Notes [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, face amount 110,000,000us-gaap_DebtInstrumentFaceAmount
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember		           110,000,000us-gaap_DebtInstrumentFaceAmount
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MediumTermNotesMember		    
Potomac Electric Power Co [Member] | First Mortgage Bonds [Member] | 4.65% Due 2014 [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, interest percentage 4.65%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_FourPointSixFivePercentageDueTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           4.65%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_FourPointSixFivePercentageDueTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		 4.65%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_FourPointSixFivePercentageDueTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		  
Repayment of first mortgage bonds               175,000,000us-gaap_RepaymentsOfFirstMortgageBond
/ us-gaap_DebtInstrumentAxis
= pom_FourPointSixFivePercentageDueTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		  
Retirement of debt 175,000,000pom_PaymentsForRetirementOfDebt
/ us-gaap_DebtInstrumentAxis
= pom_FourPointSixFivePercentageDueTwoThousandFourteenMember
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		                
Potomac Electric Power Co [Member] | First Mortgage Bonds [Member] | 3.60% Due 2024 [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, face amount 400,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointSixZeroPercentageNotesDueTwoThousandAndTwentyFourMember
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           400,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointSixZeroPercentageNotesDueTwoThousandAndTwentyFourMember
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		    
Debt instrument, maturity date Mar. 15, 2024                
Debt instrument, interest percentage 3.60%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointSixZeroPercentageNotesDueTwoThousandAndTwentyFourMember
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		           3.60%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_DebtInstrumentAxis
= pom_ThreePointSixZeroPercentageNotesDueTwoThousandAndTwentyFourMember
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_MortgagesMember		    
Potomac Electric Power Co [Member] | Senior Notes [Member]                  
Debt Instrument [Line Items]                  
Debt instrument, face amount 885,000,000us-gaap_DebtInstrumentFaceAmount
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember		           885,000,000us-gaap_DebtInstrumentFaceAmount
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_LongtermDebtTypeAxis
= us-gaap_SeniorNotesMember		    
Potomac Electric Power Co [Member] | Maximum [Member]                  
Debt Instrument [Line Items]                  
Ratio of indebtedness to total capitalization 65.00%pom_RatioOfIndebtednessToCapitalization
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		                
Ratio of deferrable interest subordinated debt to total capitalization 15.00%pom_RatioOfDeferrableInterestSubordinatedDebtToCapitalization
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		           15.00%pom_RatioOfDeferrableInterestSubordinatedDebtToCapitalization
/ dei_LegalEntityAxis
= pom_PotomacElectricPowerCoMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		    
PHI [Member] | Commercial Paper [Member]                  
Debt Instrument [Line Items]                  
Commercial paper outstanding $ 287,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_PepcoHoldingsIncMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		 $ 24,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_PepcoHoldingsIncMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember		         $ 287,000,000us-gaap_ShortTermBorrowings
/ dei_LegalEntityAxis
= pom_PepcoHoldingsIncMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_CommercialPaperMember