Lessee - Components of Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	$ 292	$ 320
Variable Lease, Cost	241	300
Short-term Lease, Cost	2	19
Total Lease Cost	535	639
Sublease Income	48	51
Exelon Generation Co L L C [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	194	222
Variable Lease, Cost	234	282
Short-term Lease, Cost	2	19
Total Lease Cost	430	523
Sublease Income	44	44
Commonwealth Edison Co [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	3	3
Variable Lease, Cost	1	2
Short-term Lease, Cost	0	0
Total Lease Cost	4	5
PECO Energy Co [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	1	1
Variable Lease, Cost	0	0
Short-term Lease, Cost	0	0
Total Lease Cost	1	1
Baltimore Gas and Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	33	33
Variable Lease, Cost	1	2
Short-term Lease, Cost	0	0
Total Lease Cost	34	35
Pepco Holdings LLC [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	46	48
Variable Lease, Cost	2	6
Short-term Lease, Cost	0	0
Total Lease Cost	48	54
Sublease Income	4	7
Finance Lease, Cost	9
Potomac Electric Power Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	11	12
Variable Lease, Cost	1	2
Short-term Lease, Cost	0	0
Total Lease Cost	12	14
Finance Lease, Cost	3
Delmarva Power & Light Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	13	14
Variable Lease, Cost	1	2
Short-term Lease, Cost	0	0
Total Lease Cost	14	16
Sublease Income	4	7
Finance Lease, Cost	4
Atlantic City Electric Company [Member]
Schedule of Components of Lease Cost [Line Items]
Operating Lease, Cost	6	7
Variable Lease, Cost	0	1
Short-term Lease, Cost	0	0
Total Lease Cost	6	$ 8
Finance Lease, Cost	$ 2