Retirement Benefits Retirement Benefits - Assumptions Used in Calculations (Details)		3 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Document Period End Date				Dec. 31, 2017
CENG Legacy Benefit Plans [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				3.66%		3.68%		3.29%
CENG Legacy Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				4.11%		4.14%		3.82%
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate				4.04%	[1]	4.29%	[2]	3.94%	[3]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets			7.00%	7.00%		7.00%	[4]	7.00%	[4]
Discount rate				3.62%	[5]	4.04%	[6]	4.29%	[7]
Pension Plan, Defined Benefit [Member] | CENG Legacy Benefit Plans [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				3.49%		3.66%		3.68%
Pension Plan, Defined Benefit [Member] | CENG Legacy Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				3.65%		4.11%		4.14%
Pension Plan, Defined Benefit [Member] | Period One [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase				3.25%
Pension Plan, Defined Benefit [Member] | Period One [Member] | CENG Legacy Benefit Plans [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase				3.25%
Pension Plan, Defined Benefit [Member] | Period Two [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase				3.75%
Pension Plan, Defined Benefit [Member] | Period Two [Member] | CENG Legacy Benefit Plans [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase				3.75%
Pension Plan, Defined Benefit [Member] | Predecessor [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Rate of compensation increase						5.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate						4.20%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	[8]	6.50%				6.50%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		5.00%				5.00%
Qualified Plan [Member] | Predecessor [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate						4.65%
Non-Qualified Pension Plan [Member] | Predecessor [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate						4.55%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Health care cost trend rate						5.50%		5.50%		6.00%
Ultimate health care cost trend rate										5.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate				4.04%	[1]	4.29%	[2]	3.92%	[3]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets			6.60%	6.58%		6.71%	[4]	6.50%	[4]
Discount rate				3.61%	[5]	4.04%	[6]	4.29%	[7]
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				4.00%		4.32%		3.99%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				4.17%		4.43%		4.06%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | CENG Legacy Benefit Plans [Member] | Minimum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				3.57%		4.00%		4.32%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Remeasurement [Member] | CENG Legacy Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Defined Benefit Plan Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate Design Changes				3.68%		4.17%		4.43%
Other Postretirement Benefit Plan, Defined Benefit [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Health care cost trend rate						5.40%		5.40%		5.50%
Ultimate health care cost trend rate										5.00%
DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYearAge				0.0633		0.0633		0.0667
Other Postretirement Benefit Plan, Defined Benefit [Member] | Predecessor [Member] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Rate of compensation increase						5.00%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		4.55%				4.15%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	[8]	6.75%				6.75%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		5.00%				5.00%
Discount rate						4.55%

[1] )The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2017. Certain benefit plans used individual rates ranging from 3.66%-4.11% and 4.00%-4.17% for pension and other postretirement plans, respectivel

[2] The discount rates above represent the blended rates used to establish the majority of Exelon's pension and other postretirement benefits costs for the year ended December 31, 2016. Certain benefit plans used individual rates ranging from 3.68%-4.14% and 4.32%-4.43% for pension and other postretirement plans, respectively.

[3] The discount rates above represent the blended rates used to establish the majority of Exelon’s pension and other postretirement benefits costs for the year ended December 31, 2015. Certain benefit plans used the individual rates ranging from 3.29%-3.82% and 3.99%-4.06% for pension and other postretirement plans, respectively.

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

[5] The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2017. Certain benefit plans used individual rates ranging from 3.49% - 3.65% and 3.57% - 3.68% for pension and other postretirement plans, respectively.

[6] The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2016. Certain benefit plans used individual rates ranging from 3.66% - 4.11% and 4.00% - 4.17% for pension and other postretirement plans, respectively.

[7] The discount rates above represent the blended rates used to determine the majority of Exelon’s pension and other postretirement benefits obligations as of December 31, 2015. Certain benefit plans used individual rates ranging from 3.68% - 4.14% and 4.32% - 4.43% for pension and other postretirement plans, respectively.

[8] Expected return on other postretirement benefit plan assets is pre-tax.