Retirement Benefits - Assumptions Used In Calculations (Details)	3 Months Ended
	Mar. 31, 2013
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	3.92%
Other Postretirement Benefit Plans Defined Benefit [Member] | Exelon Legacy Benefit Plans [Member]
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Net Periodic Benefit Cost [Abstract]
Expected return on plan assets	6.45%
Discount rate	4.00%