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Derivative Financial Instruments (Commodity Price Risk) (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2012
GWH
Sep. 30, 2011
GWH
Sep. 30, 2012
MW
GWH
Sep. 30, 2011
GWH
Exelon Generation Co L L C [Member]
       
Swap Contract Volumes [Abstract]        
Swap contract volumes     3,000  
Proprietary Trading Volumes [Abstract]        
Proprietary trading activities volume 4,352 1,679 9,981 4,508
Exelon Generation Co L L C [Member] | One Year From Balance Sheet Date [Member]
       
Percent Of Expected Generation Being Hedged [Abstract]        
Minimum range of expected generation hedged     98.00%  
Maximum range of expected generation hedged     101.00%  
Exelon Generation Co L L C [Member] | More Than One And Within Two Years From Balance Sheet Date [Member]
       
Percent Of Expected Generation Being Hedged [Abstract]        
Minimum range of expected generation hedged     87.00%  
Maximum range of expected generation hedged     90.00%  
Exelon Generation Co L L C [Member] | More Than Two And Within Three Years From Balance Sheet Date [Member]
       
Percent Of Expected Generation Being Hedged [Abstract]        
Minimum range of expected generation hedged     55.00%  
Maximum range of expected generation hedged     58.00%  
Exelon Generation Co L L C [Member] | More Than Three And Within Four Years From Balance Sheet Date [Member]
       
Percent Of Expected Generation Being Hedged [Abstract]        
Minimum range of expected generation hedged     20000000.00%  
Maximum range of expected generation hedged     23000000.00%  
PECO Energy Co [Member]
       
Percent Of Gas Purchases Being Hedged [Abstract]        
Estimated percentage of natural gas purchases hedged     30.00%