Commitments and Contingencies - Schedule of Minimum Future Operating Lease Payments (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Operating Leases Future Minimum Payments Due [Line Items]
2015	$ 99
2016	102
2017	102
2018	86
2019	70
Remaining years	699
Total minimum future lease payments	1,158	[1]
Exelon Generation Co L L C [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2015	51	[2]
2016	57	[2]
2017	63	[2]
2018	57	[2]
2019	43	[2]
Remaining years	628	[2]
Total minimum future lease payments	899	[1],[2]
Exelon Generation Co L L C [Member] | Baltimore Headquarters [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2015	0
2016	5
2017	12
2018	13
2019	13
Remaining years	285
Commonwealth Edison Co [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2015	14	[3]
2016	13	[3]
2017	8	[3]
2018	4	[3]
2019	4	[3]
Remaining years	2	[3]
Total minimum future lease payments	45	[3]
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]
2015	3	[3]
2016	3	[3]
2017	3	[3]
2018	3	[3]
2019	2	[3]
Remaining years	0	[3]
Total minimum future lease payments	14	[3]
PECO Energy Co [Member] | Real Estate Leases and Railroad Licenses [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments	3
Baltimore Gas and Electric Company [Member]
Operating Leases Future Minimum Payments Due [Line Items]
2015	13	[3],[4]
2016	11	[3],[4]
2017	10	[3],[4]
2018	9	[3],[4]
2019	7	[3],[4]
Remaining years	27	[3],[4]
Total minimum future lease payments	77	[3],[4]
Baltimore Gas and Electric Company [Member] | Baltimore Headquarters [Member]
Operating Leases Future Minimum Payments Due [Line Items]
Total minimum future lease payments	328
Term of lease	20 years
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	$ 2

[1] Excludes Generation’s PPAs and tolling arrangements that are accounted for as contingent operating lease payments, since these expected cash outflows are already disclosed in the Net Capacity Purchases table under the Energy Commitment.

[2] The Generation column above now includes minimum future lease payments associated with a 20-year lease agreement for the Baltimore headquarters that became effective during the second quarter of 2014. Generation’s total commitments under the lease agreement are $0 in 2015, and $5 million, $12 million, $13 million, $13 million, and $285 million related to years 2016, 2017, 2018, 2019, and thereafter, respectively, for a total of $328 million .

[3] Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO and BGE have excluded these payments from the remaining years, as such amounts would not be meaningful. ComEd’s, PECO’s, and BGE’s annual obligation for these arrangements, included in each of the years 2015—2019, was $2 million, $3 million, and $2 million respectively.

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