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Consolidated Statement of Changes in Shareholders Equity (Unaudited) (Parenthetical) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Other comprehensive income, income taxes $ 192us-gaap_OtherComprehensiveIncomeLossTax
Exelon Generation Co L L C [Member]  
Other comprehensive income, income taxes 263us-gaap_OtherComprehensiveIncomeLossTax
/ dei_LegalEntityAxis
= exc_ExelonGenerationCoLLCMember
PECO Energy Co [Member]  
Other comprehensive income, income taxes 0us-gaap_OtherComprehensiveIncomeLossTax
/ dei_LegalEntityAxis
= exc_PecoEnergyCoMember
Commonwealth Edison Co [Member]  
Other comprehensive income, income taxes $ 0us-gaap_OtherComprehensiveIncomeLossTax
/ dei_LegalEntityAxis
= exc_CommonwealthEdisonCoMember