Retirement Benefits - Assumptions Used In Calculations (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Sep. 30, 2012
Pension Plans Defined Benefit [Member]
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Net Periodic Benefit Cost [Abstract]
Expected return on plan assets			7.50%
Discount rate	3.97%		4.74%
Discount rate from acquisition entity		4.27%
Other Postretirement Benefit Plans Defined Benefit [Member]
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Net Periodic Benefit Cost [Abstract]
Expected return on plan assets			6.68%
Discount rate	3.98%		4.80%
Discount rate from acquisition entity		4.28%
Other Postretirement Benefit Plans Defined Benefit [Member] | Exelon Legacy Benefit Plans [Member]
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Benefit Obligation [Abstract]
Discount rate	3.93%		3.93%
Other Postretirement Benefit Plans Defined Benefit [Member] | Constellation Legacy Benefit Plans [Member]
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Benefit Obligation [Abstract]
Discount rate	3.72%		3.72%