Retirement Benefits - Additional (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014
Defined Benefit Plan Contributions [Abstract]
Expected qualified pension plan contributions	$ 317
Expected non-qualified pension plan contributions	18
Expected other postretirement benefit plan contributions	290
Business Services Company [Member] | CENGMember [Member]
Defined Benefit Plan Contributions [Abstract]
Expected qualified pension plan contributions	51
Exelon Generation Co L L C [Member]
Defined Benefit Plan Contributions [Abstract]
Expected qualified pension plan contributions	169
Expected non-qualified pension plan contributions	9
Expected other postretirement benefit plan contributions	128
Exelon Generation Co L L C [Member] | CENGMember [Member]
Defined Benefit Plan Contributions [Abstract]
Expected qualified pension plan contributions	53
Expected non-qualified pension plan contributions	3
Expected other postretirement benefit plan contributions	5
Commonwealth Edison Co [Member]
Defined Benefit Plan Contributions [Abstract]
Expected qualified pension plan contributions	119
Expected non-qualified pension plan contributions	1
Expected other postretirement benefit plan contributions	121
PECO Energy Co [Member]
Defined Benefit Plan Contributions [Abstract]
Expected qualified pension plan contributions	11
Expected other postretirement benefit plan contributions	4
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Contributions [Abstract]
Expected non-qualified pension plan contributions	1
Expected other postretirement benefit plan contributions	$ 18