Lessee - 2018 Schedule of Minimum Future Operating Lease Payments (Details) $ in Millions	Dec. 31, 2018 USD ($)
Operating Leases Future Minimum Payments Due [Line Items]
2019	$ 140
2020	149
2021	143
2022	126
2023	97
Remaining Years	723
Total Minimum Future Lease Payments	1,378
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	33
2020	46
2021	46
2022	47
2023	46
Remaining Years	545
Total Minimum Future Lease Payments	763
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	7
2020	5
2021	4
2022	4
2023	3
Remaining Years	0
Total Minimum Future Lease Payments	23
PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	5
2020	5
2021	5
2022	5
2023	5
Remaining Years	0
Total Minimum Future Lease Payments	25
Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	35
2020	35
2021	33
2022	18
2023	3
Remaining Years	19
Total Minimum Future Lease Payments	143
Pepco Holdings LLC [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	48
2020	46
2021	43
2022	42
2023	39
Remaining Years	159
Total Minimum Future Lease Payments	377
Potomac Electric Power Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	11
2020	10
2021	9
2022	8
2023	8
Remaining Years	40
Total Minimum Future Lease Payments	86
Delmarva Power & Light Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	14
2020	13
2021	12
2022	12
2023	10
Remaining Years	35
Total Minimum Future Lease Payments	96
Atlantic City Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	7
2020	6
2021	5
2022	5
2023	4
Remaining Years	5
Total Minimum Future Lease Payments	32
Real Estate Leases and Railroad Licenses [Member] | Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total Minimum Future Lease Payments	3
Real Estate Leases and Railroad Licenses [Member] | PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total Minimum Future Lease Payments	5
Real Estate Leases and Railroad Licenses [Member] | Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total Minimum Future Lease Payments	1
Real Estate Leases and Railroad Licenses [Member] | Delmarva Power & Light Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total Minimum Future Lease Payments	1
Electrical Conduit System [Member] | Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2019	26
2020	28
2021	28
2022	$ 14