Leases Lessee Future Minimum Operating Lease Maturity Payments (Details) $ in Millions	Mar. 31, 2019 USD ($)
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	$ 214
2020	289
2021	244
2022	174
2023	139
Remaining Years	1,052
Lessee, Operating Lease, Liability, Payments, Due	2,112
Interest	468
Operating Lease, Liability	1,644	[1]
Exelon Generation Co L L C [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	154
2020	202
2021	162
2022	112
2023	99
Remaining Years	840
Lessee, Operating Lease, Liability, Payments, Due	1,569
Interest	373
Operating Lease, Liability	1,196	[1]
Commonwealth Edison Co [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	2
2020	2
2021	2
2022	1
2023	0
Remaining Years	0
Lessee, Operating Lease, Liability, Payments, Due	7
Interest	0
Operating Lease, Liability	7
PECO Energy Co [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	1
2020	1
2021	0
2022	0
2023	0
Remaining Years	0
Lessee, Operating Lease, Liability, Payments, Due	2
Interest	0
Operating Lease, Liability	2
Baltimore Gas and Electric Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	19
2020	34
2021	32
2022	16
2023	0
Remaining Years	18
Lessee, Operating Lease, Liability, Payments, Due	119
Interest	22
Operating Lease, Liability	97
Pepco Holdings LLC [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	33
2020	43
2021	42
2022	40
2023	39
Remaining Years	194
Lessee, Operating Lease, Liability, Payments, Due	391
Interest	71
Operating Lease, Liability	320
Potomac Electric Power Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	8
2020	9
2021	9
2022	8
2023	8
Remaining Years	42
Lessee, Operating Lease, Liability, Payments, Due	84
Interest	16
Operating Lease, Liability	68
Delmarva Power and Light Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	7
2020	12
2021	11
2022	11
2023	10
Remaining Years	52
Lessee, Operating Lease, Liability, Payments, Due	103
Interest	20
Operating Lease, Liability	83
Atlantic City Electric Company [Member]
Schedule of Lessee, Operating Lease, Liability, Maturity [Line Items]
2019	5
2020	5
2021	5
2022	4
2023	3
Remaining Years	7
Lessee, Operating Lease, Liability, Payments, Due	29
Interest	3
Operating Lease, Liability	$ 26

[1] Exelon's and Generation's operating ROU assets and lease liabilities include $631 million and $778 million, respectively, related to contracted generation.