Commitments and Contingencies Commitments and Contingencies - Schedule of Minimum Future Operating Lease Payments (Details) - USD ($) $ in Millions		Dec. 31, 2017		Nov. 30, 2016
Operating Leases Future Minimum Payments Due [Line Items]
2018	[1]	$ 188
2019	[1]	129
2020	[1]	147
2021	[1]	142
2022	[1]	119
Remaining Years	[1]	787
Total minimum future lease payments	[1]	1,512
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2018	[1]	74
2019	[1]	29
2020	[1]	47
2021	[1]	48
2022	[1]	46
Remaining Years	[1]	573
Total minimum future lease payments	[1]	817
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2018	[2]	7
2019	[2]	6
2020	[2]	4
2021	[2]	4
2022	[2]	2
Remaining Years	[2]	0
Total minimum future lease payments	[2]	23
Commonwealth Edison Co [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments		2
PECO Energy Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2018	[2]	5
2019	[2]	5
2020	[2]	5
2021	[2]	5
2022	[2]	5
Remaining Years	[2]	0
Total minimum future lease payments	[2]	25
PECO Energy Co [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments		5
Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2018		34	[2],[3],[4]	$ 25
2019		34	[2],[3],[4]	26
2020		34	[2],[3],[4]	28
2021		32	[2],[3],[4]	28
2022		17	[2],[3],[4]	$ 14
Remaining Years	[2],[3],[4]	19
Total minimum future lease payments	[2],[3],[4]	170
Baltimore Gas and Electric Company [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments		1
Pepco Holdings LLC [Member] | Successor [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2018		56
2019		42
2020		44
2021		40
2022		39
Remaining Years		194
Total minimum future lease payments		415
Potomac Electric Power Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2018		8
2019		7
2020		6
2021		5
2022		4
Remaining Years		8
Total minimum future lease payments		38
Delmarva Power and Light Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2018	[2]	20
2019	[2]	10
2020	[2]	13
2021	[2]	12
2022	[2]	12
Remaining Years	[2]	54
Total minimum future lease payments	[2]	121
Delmarva Power and Light Company [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments		2
Atlantic City Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2018		9
2019		8
2020		8
2021		7
2022		6
Remaining Years		19
Total minimum future lease payments		$ 57

[1] Excludes Generation’s contingent operating lease payments associated with contracted generation agreements.

[2] Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO, BGE and DPL have excluded these payments from the remaining years as such amounts would not be meaningful. ComEd’s, PECO’s, BGE’s and DPL's average annual obligation for these arrangements, included in each of the years 2018—2022, was $2 million, $5 million, $1 million and $2 million, respectively.

[3] Includes all future lease payments on a 99-year real estate lease that expires in 2106.

[4] The BGE column above includes minimum future lease payments associated with a 6-year lease for the Baltimore City conduit system that became effective during the fourth quarter of 2016. BGE's total commitments under the lease agreement are $25 million, $26 million, $28 million , $28 million and $14 million related to years 2018, 2019, 2020, 2021and 2022, respectively.