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Regulatory Matters - Estimated Commitments related to PJM Agreements (Details) (Construction Expansion Plans [Member], USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Commonwealth Edison Co [Member]
 
Other Commitments [Line Items]  
Total $ 335us-gaap_OtherCommitment
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_CommonwealthEdisonCoMember
2015 150us-gaap_OtherCommitmentDueInNextTwelveMonths
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_CommonwealthEdisonCoMember
2016 172us-gaap_OtherCommitmentDueInSecondYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_CommonwealthEdisonCoMember
2017 5us-gaap_OtherCommitmentDueInThirdYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_CommonwealthEdisonCoMember
2018 4us-gaap_OtherCommitmentDueInFourthYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_CommonwealthEdisonCoMember
2019 4us-gaap_OtherCommitmentDueInFifthYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_CommonwealthEdisonCoMember
PECO Energy Co [Member]
 
Other Commitments [Line Items]  
Total 100us-gaap_OtherCommitment
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_PecoEnergyCoMember
2015 32us-gaap_OtherCommitmentDueInNextTwelveMonths
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_PecoEnergyCoMember
2016 31us-gaap_OtherCommitmentDueInSecondYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_PecoEnergyCoMember
2017 25us-gaap_OtherCommitmentDueInThirdYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_PecoEnergyCoMember
2018 8us-gaap_OtherCommitmentDueInFourthYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_PecoEnergyCoMember
2019 4us-gaap_OtherCommitmentDueInFifthYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_PecoEnergyCoMember
Baltimore Gas and Electric Company [Member]
 
Other Commitments [Line Items]  
Total 351us-gaap_OtherCommitment
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_BaltimoreGasAndElectricCompanyMember
2015 77us-gaap_OtherCommitmentDueInNextTwelveMonths
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_BaltimoreGasAndElectricCompanyMember
2016 104us-gaap_OtherCommitmentDueInSecondYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_BaltimoreGasAndElectricCompanyMember
2017 77us-gaap_OtherCommitmentDueInThirdYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_BaltimoreGasAndElectricCompanyMember
2018 57us-gaap_OtherCommitmentDueInFourthYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_BaltimoreGasAndElectricCompanyMember
2019 $ 36us-gaap_OtherCommitmentDueInFifthYear
/ exc_ConstructionProjectAxis
= exc_ConstructionExpansionPlansMember
/ dei_LegalEntityAxis
= exc_BaltimoreGasAndElectricCompanyMember