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Derivative Financial Instruments (Commodity Price Risk) (Details)
3 Months Ended
Mar. 31, 2013
GWh
Mar. 31, 2012
GWh
Exelon Generation Co L L C [Member]
   
Proprietary Trading Volumes [Abstract]    
Proprietary trading activities volume 1,572 1,888
Exelon Generation Co L L C [Member] | Minimum [Member]
   
Percent Of Expected Generation Being Hedged [Abstract]    
Expected generation hedged in next twelve months 98.00%  
Expected generation hedged in year two 70.00%  
Expected generation hedged in year three 33.00%  
Exelon Generation Co L L C [Member] | Maximum [Member]
   
Percent Of Expected Generation Being Hedged [Abstract]    
Expected generation hedged in next twelve months 101.00%  
Expected generation hedged in year two 73.00%  
Expected generation hedged in year three 36.00%  
PECO Energy Co [Member]
   
Percent Of Gas Purchases Being Hedged [Abstract]    
Estimated percentage of natural gas purchases hedged 30.00%  
Baltimore Gas and Electric Company [Member] | Minimum [Member]
   
Percent Of Gas Purchases Being Hedged [Abstract]    
Estimated percentage of natural gas purchases hedged 10.00%  
Baltimore Gas and Electric Company [Member] | Maximum [Member]
   
Percent Of Gas Purchases Being Hedged [Abstract]    
Estimated percentage of natural gas purchases hedged 20.00%