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Retirement Benefits - Additional (Details) (USD $)
In Millions, unless otherwise specified
Jun. 30, 2013
Defined Benefit Plan Contributions [Abstract]  
Expected qualified pension plan contributions $ 255
Expected non-qualified pension plan contributions 81
Expected other postretirement benefit plan contributions 276
Exelon Generation Co L L C [Member]
 
Defined Benefit Plan Contributions [Abstract]  
Expected qualified pension plan contributions 113
Expected non-qualified pension plan contributions 7
Expected other postretirement benefit plan contributions 108
Commonwealth Edison Co [Member]
 
Defined Benefit Plan Contributions [Abstract]  
Expected qualified pension plan contributions 115
Expected non-qualified pension plan contributions 1
Expected other postretirement benefit plan contributions 112
PECO Energy Co [Member]
 
Defined Benefit Plan Contributions [Abstract]  
Expected non-qualified pension plan contributions 1
Expected other postretirement benefit plan contributions 21
Baltimore Gas and Electric Company [Member]
 
Defined Benefit Plan Contributions [Abstract]  
Expected qualified pension plan contributions 11
Expected non-qualified pension plan contributions 2
Expected other postretirement benefit plan contributions $ 17