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Investment in Constellation Energy Nuclear Group, LLC (Tables)
3 Months Ended
Mar. 31, 2012
Equity Method Investments and Joint Ventures Tables [Line Items]  
Schedule of total equity in earnings of investment in CENG
  For the Period
  March 12 through March 31,
 2012
CENG$(9)
Amortization of basis difference in CENG (12)
Total equity investment losses - CENG$(21)
Schedule of summarized income statement information for CENG ##RS
Exelon Generation Co L L C [Member]
 
Equity Method Investments and Joint Ventures Tables [Line Items]  
Schedule of total equity in earnings of investment in CENG
  For the Period
  March 12 through March 31,
 2012
CENG$(9)
Amortization of basis difference in CENG (12)
Total equity investment losses - CENG$(21)