Retirement Benefits - Assumptions Used in Calculations (Details)	0 Months Ended	12 Months Ended						1 Months Ended	0 Months Ended
	Oct. 31, 2014	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Apr. 30, 2014	Apr. 30, 2014
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate		3.94%		4.80%		3.92%
Discount rate	3.95%	4.80%	[1]	3.92%	[2]	4.74%	[3]
Expected return on plan assets	7.00%	7.00%	[4]	7.50%	[4]	7.50%	[4]
Rate of compensation increase						3.75%
Pension Plan, Defined Benefit [Member] | Remeasurement [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Expected return on plan assets								6.59%
Discount rate used for remeasurement due to design changes				4.21%		3.71%
Pension Plan, Defined Benefit [Member] | First Five Years [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Rate of compensation increase		3.25%				3.25%
Rate of compensation increase		3.25%		3.25%
Pension Plan, Defined Benefit [Member] | Thereafter [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Rate of compensation increase		3.75%				3.75%
Rate of compensation increase		3.75%		3.75%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate		3.92%		4.90%		4.00%
Discount rate		4.90%	[1]	4.00%	[2]	4.80%	[3]		4.30%
Expected return on plan assets		6.59%	[4]	6.45%	[4]	6.68%	[4]		6.59%
Rate of compensation increase						3.75%
Health care cost trend rate		6.00%		6.50%		6.50%
Ultimate health care cost trend rate		5.00%		5.00%		5.00%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate used for remeasurement due to design changes				4.66%		3.72%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate used for remeasurement due to design changes		4.09%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate used for remeasurement due to design changes		4.55%
CENG Legacy Benefit Plans [Member] | Remeasurement [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate used for remeasurement due to design changes		3.60%
CENG Legacy Benefit Plans [Member] | Remeasurement [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate used for remeasurement due to design changes		4.30%

[1] )The discount rates above represent the initial discount rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2014. Certain of the other postretirement benefit plans were remeasured as of April 30, 2014 using an expected long-term rate of return on plan assets of 6.59% and a discount rate of 4.30%. Costs for the year ended December 31, 2014 reflect the impact of this remeasurement. On April 1, 2014, Generation assumed operational control of CENG’s nuclear fleet. As a result, Exelon became the sponsor of CENG’s legacy pension and OPEB plans effective July 14, 2014; discount rates for those plans, impacting 2014 costs, ranged from 3.60%-4.30% and 4.09%-4.55%, respectivel

[2] The discount rates above represent the initial discount rates used to establish Exelon's pension and other postretirement benefits costs for the year ended December 31, 2013. Certain of the benefit plans were remeasured during the year using discount rates of 4.21% and 4.66% for pension and other postretirement benefits, respectively. Costs for the year ended December 31, 2013 reflect the impact of these measurements

[3] The discount rates above represent the initial discounts rates used to establish Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2012. Certain of the benefit plans were remeasured during the year due to the Constellation merger, plan settlement and curtailment events, and plan changes using discount rates of 3.71% and 3.72% for pension and other postretirement benefits, respectively. Costs for the year ended December 31, 2012 reflect the impact of these remeasurement

[4] Not applicable to pension and other postretirement benefit plans that do not have plan asset