Retirement Benefits - Additional (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Defined Benefit Plan Contributions [Abstract]
Expected qualified pension plan contributions	$ 264
Expected non-qualified pension plan contributions	12
Expected other postretirement benefit plan contributions	430
Exelon Generation Co L L C [Member]
Defined Benefit Plan Contributions [Abstract]
Expected qualified pension plan contributions	118
Expected non-qualified pension plan contributions	5
Expected other postretirement benefit plan contributions	168
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	197
PECO Energy Co [Member]
Defined Benefit Plan Contributions [Abstract]
Expected qualified pension plan contributions	11
Expected other postretirement benefit plan contributions	19
Baltimore Gas and Electric Company [Member]
Defined Benefit Plan Contributions [Abstract]
Expected non-qualified pension plan contributions	1
Expected other postretirement benefit plan contributions	$ 17