Lessee - Lessee Future Minimum Operating Lease Maturity Payments (Details) $ in Millions	Dec. 31, 2019 USD ($)
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	$ 287
2021	243
2022	177
2023	145
2024	140
Remaining years	976
Lessee, Operating Lease, Liability, Payments, Due	1,968
Interest	436
Operating Lease, Liability	1,532
Exelon Generation Co L L C [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	203
2021	162
2022	113
2023	100
2024	97
Remaining years	741
Lessee, Operating Lease, Liability, Payments, Due	1,416
Interest	334
Operating Lease, Liability	1,082
Commonwealth Edison Co [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	3
2021	4
2022	2
2023	1
2024	1
Remaining years	1
Lessee, Operating Lease, Liability, Payments, Due	12
Interest	1
Operating Lease, Liability	11
PECO Energy Co [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	0
2021	1
2022	0
2023	0
2024	0
Remaining years	0
Lessee, Operating Lease, Liability, Payments, Due	1
Interest	0
Operating Lease, Liability	1
Baltimore Gas and Electric Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	34
2021	31
2022	16
2023	1
2024	0
Remaining years	18
Lessee, Operating Lease, Liability, Payments, Due	100
Interest	18
Operating Lease, Liability	82
Pepco Holdings LLC [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	42
2021	41
2022	38
2023	37
2024	35
Remaining years	153
Lessee, Operating Lease, Liability, Payments, Due	346
Interest	61
Operating Lease, Liability	285
Potomac Electric Power Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	8
2021	8
2022	8
2023	7
2024	5
Remaining years	34
Lessee, Operating Lease, Liability, Payments, Due	70
Interest	13
Operating Lease, Liability	57
Delmarva Power & Light Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	11
2021	11
2022	10
2023	9
2024	9
Remaining years	41
Lessee, Operating Lease, Liability, Payments, Due	91
Interest	17
Operating Lease, Liability	74
Atlantic City Electric Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2020	5
2021	4
2022	4
2023	3
2024	2
Remaining years	2
Lessee, Operating Lease, Liability, Payments, Due	20
Interest	2
Operating Lease, Liability	$ 18