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Goodwill - Additional Information (Detail) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Goodwill [Line Items]    
Goodwill $ 1,407,000,000us-gaap_Goodwill $ 1,407,000,000us-gaap_Goodwill
Accumulated impairment loss 18,000,000us-gaap_GoodwillImpairedAccumulatedImpairmentLoss 18,000,000us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
Delmarva Power & Light Co/De [Member]    
Goodwill [Line Items]    
Goodwill 8,000,000us-gaap_Goodwill
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		 8,000,000us-gaap_Goodwill
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember
Accumulated impairment loss $ 0us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember		 $ 0us-gaap_GoodwillImpairedAccumulatedImpairmentLoss
/ dei_LegalEntityAxis
= pom_DelmarvaPowerLightCoMember