Retirement Benefits - Assumptions Used in Calculations (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	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	4.13%	3.49%	3.66%
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	4.36%	3.65%	4.11%
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate - Obligation	3.34%	4.31%
Benefit Obligation Investment Crediting Rate	3.82%	4.46%
Discount rate - Net Periodic Benefit Costs	4.31%	3.62%	4.04%
Net Periodic Benefit Cost Investment Crediting Rate	4.46%	4.00%	4.46%
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%
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	3.02%	4.13%
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	3.44%	4.36%
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 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] | Pepco Holdings LLC [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Rate of compensation increase		5.00%
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Assumptions Used In Calculations [Line Items]
Discount rate - Obligation	3.31%	4.30%
Health care cost trend rate	5.00%	5.00%	5.50%
Ultimate health care cost trend rate	5.00%	5.00%	5.00%
Discount rate - Net Periodic Benefit Costs	4.30%	3.61%	4.04%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	6.67%	6.60%	6.58%
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	4.27%	3.57%	4.00%
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	4.38%	3.68%	4.17%
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	3.27%	4.27%
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	3.40%	4.38%