Lessee - Components of Lease Cost (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	$ 320
Variable Lease, Cost	300
Short-term Lease, Cost	19
Total Lease Cost	639
Sublease Income	$ 51
Operating Lease, Weighted Average Remaining Lease Term	10 years 1 month 6 days
Operating Lease, Weighted Average Discount Rate, Percent	4.60%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 52
Exelon Generation Co L L C [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	222
Variable Lease, Cost	282
Short-term Lease, Cost	19
Total Lease Cost	523
Sublease Income	$ 44
Operating Lease, Weighted Average Remaining Lease Term	10 years 7 months 6 days
Operating Lease, Weighted Average Discount Rate, Percent	4.80%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 14
Commonwealth Edison Co [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	3
Variable Lease, Cost	2
Short-term Lease, Cost	0
Total Lease Cost	$ 5
Operating Lease, Weighted Average Remaining Lease Term	4 years 7 months 6 days
Operating Lease, Weighted Average Discount Rate, Percent	3.00%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 6
PECO Energy Co [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	1
Variable Lease, Cost	0
Short-term Lease, Cost	0
Total Lease Cost	$ 1
Operating Lease, Weighted Average Remaining Lease Term	4 years 4 months 24 days
Operating Lease, Weighted Average Discount Rate, Percent	3.20%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 0
Baltimore Gas and Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	33
Variable Lease, Cost	2
Short-term Lease, Cost	0
Total Lease Cost	$ 35
Operating Lease, Weighted Average Remaining Lease Term	5 years 4 months 24 days
Operating Lease, Weighted Average Discount Rate, Percent	3.60%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ 2
Pepco Holdings LLC [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	48
Variable Lease, Cost	6
Short-term Lease, Cost	0
Total Lease Cost	54
Sublease Income	$ 7
Operating Lease, Weighted Average Remaining Lease Term	9 years
Operating Lease, Weighted Average Discount Rate, Percent	4.20%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ (3)
Potomac Electric Power Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	12
Variable Lease, Cost	2
Short-term Lease, Cost	0
Total Lease Cost	$ 14
Operating Lease, Weighted Average Remaining Lease Term	9 years 9 months 18 days
Operating Lease, Weighted Average Discount Rate, Percent	4.00%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ (1)
Delmarva Power & Light Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	14
Variable Lease, Cost	2
Short-term Lease, Cost	0
Total Lease Cost	16
Sublease Income	$ 7
Operating Lease, Weighted Average Remaining Lease Term	9 years 8 months 12 days
Operating Lease, Weighted Average Discount Rate, Percent	4.00%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ (2)
Atlantic City Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	7
Variable Lease, Cost	1
Short-term Lease, Cost	0
Total Lease Cost	$ 8
Operating Lease, Weighted Average Remaining Lease Term	4 years 8 months 12 days
Operating Lease, Weighted Average Discount Rate, Percent	3.60%
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	$ (1)