Intangible Assets - Schedule of Other Intangible Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended		1 Months Ended
	Dec. 31, 2014		Feb. 28, 2003	Dec. 31, 2010 MW	Sep. 30, 2011 MW
Finite-Lived Intangible Assets [Line Items]
Gross	2,489
Accumulated Amortization	(1,751)
Net	738
2015	66
Finite-Lived Intangible Assets, Amortization Expense, Year Two	39
2017	40
2018	69
2019	67
Other miscellaneous unamortized energy contracts	26
Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	10 years
Commonwealth Edison Co [Member]
Finite-Lived Intangible Assets [Line Items]
Chicago payment made to city			60
Period for payment			10 years
City of Chicago payment made to 3rd party			(2)
City of Chicago payment received			32
Reduction of amortization expense			(2)
Commonwealth Edison Co [Member] | Intangible Asset Nineteen Ninety Nine Chicago Settlement Agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	21 years 9 months 18 days	[1],[2]
Gross	100	[1]
Accumulated Amortization	(79)	[1]
Net	21	[1]
2015	3	[1]
Finite-Lived Intangible Assets, Amortization Expense, Year Two	3	[1]
2017	4	[1]
2018	4	[1]
2019	4	[1]
Commonwealth Edison Co [Member] | Intangible Asset Two Thousand Three Chicago Settlement Agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	17 years 10 months 24 days	[2],[3]
Gross	62	[3]
Accumulated Amortization	(40)	[3]
Net	22	[3]
2015	4	[3]
Finite-Lived Intangible Assets, Amortization Expense, Year Two	4	[3]
2017	3	[3]
2018	3	[3]
2019	3	[3]
Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
2015	4
Finite-Lived Intangible Assets, Amortization Expense, Year Two	3
2017	0
2018	2
2019	2
Exelon Wind Acquisition [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Wind turbine supply megawatt				735
Exelon Wind Acquisition [Member] | Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	18 years	[2],[4],[5]
Gross	224	[4],[5]
Accumulated Amortization	(55)	[4],[5]
Net	169
2015	14	[4],[5]
Finite-Lived Intangible Assets, Amortization Expense, Year Two	14	[4],[5]
2017	14	[4],[5]
2018	14	[4],[5]
2019	14	[4],[5]
Antelope Valley Acquisition [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Wind turbine supply megawatt					230
Antelope Valley Acquisition [Member] | Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	25 years	[2],[4],[6]
Gross	190	[4],[6]
Accumulated Amortization	(12)	[4],[6]
Net	178
2015	8	[4],[6]
Finite-Lived Intangible Assets, Amortization Expense, Year Two	8	[4],[6]
2017	8	[4],[6]
2018	8	[4],[6]
2019	8	[4],[6]
Constellation Energy Group LLC [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	1 year 5 months 24 days
Gross	1,499
Accumulated Amortization	(1,451)
Net	48
2015	19
Finite-Lived Intangible Assets, Amortization Expense, Year Two	(31)
2017	(21)
2018	11
2019	8
Constellation Energy Group LLC [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	10 years
Gross	243
Accumulated Amortization	(79)
Net	164
2015	23
Finite-Lived Intangible Assets, Amortization Expense, Year Two	23
2017	23
2018	23
2019	23
Constellation Energy Group LLC [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	12 years 4 months 24 days
Gross	214
Accumulated Amortization	(58)
Net	156
2015	18
Finite-Lived Intangible Assets, Amortization Expense, Year Two	18
2017	18
2018	18
2019	17
CENG [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	1 year 8 months 12 days
Gross	(97)
Accumulated Amortization	29
Net	(68)
2015	(20)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	(11)
2017	(15)
2018	(18)
2019	(15)
Integrys [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	2 years 4 months 24 days
Gross	6
Accumulated Amortization	(5)
Net	1
2015	(8)
Finite-Lived Intangible Assets, Amortization Expense, Year Two	6
2017	1
2018	1
2019	0
Integrys [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	10 years
Gross	48
Accumulated Amortization	(1)
Net	47
2015	5
Finite-Lived Intangible Assets, Amortization Expense, Year Two	5
2017	5
2018	5
2019	5

[1] In September 2011, Generation acquired all of the interest in Antelope Valley Solar Ranch One, a 230 MW solar project under development in northern Los Angeles County, CA from First Solar, Inc.

[2] See Note 5—Investment in Constellation Energy Nuclear Group, LLC for additional information.

[3] See Note 4—Mergers, Acquisitions, and Dispositions for further information on these acquisitions.

[4] In March 1999, ComEd entered into a settlement agreement with the City of Chicago associated with ComEd’s franchise agreement. Under the terms of the settlement, ComEd agreed to make payments to the City of Chicago each year from 1999 to 2002. The intangible asset recognized as a result of these payments is being amortized ratably over the remaining term of the franchise agreement, which ends in 2020.

[5] Includes unamortized energy contract assets and liabilities on Exelon's and Generation's Consolidated Balance Sheets. Excludes $26 million of other miscellaneous unamortized energy contracts that have been acquired at various points in time. The estimated amortization for these miscellaneous unamortized energy contracts is $4 million, $3 million, $0 million, $2 million and $2 million for 2015, 2016, 2017, 2018 and 2019, respectively.

[6] In December 2010, Generation acquired all of the equity interests of John Deere Renewables, LLC (later named Exelon Wind), adding 735MWs of installed, operating wind capacity located in eight states.