Intangible Assets - Schedule of Other Intangible Assets (Details) $ in Millions		1 Months Ended			12 Months Ended
		Sep. 30, 2011 MW	Dec. 31, 2010 MW	Feb. 28, 2003 USD ($)	Dec. 31, 2016 USD ($)
Finite-Lived Intangible Assets [Line Items]
Gross					$ 1,225
Accumulated Amortization					(1,504)
Net					(279)
2017					244
2018					(101)
2019					38
2020					30
2021					$ (11)
Licensing Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[1],[2]				10 years
Gross	[1]				$ 95
Accumulated Amortization	[1]				(15)
Net	[1]				80
2017	[1]				(10)
2018	[1]				10
2019	[1]				(10)
2020	[1]				(10)
2021	[1]				10
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Net	[3],[4]				11
2017					$ (1)
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	[2],[5]				21 years 9 months 18 days
Gross	[5]				$ 100
Accumulated Amortization	[5]				(86)
Net	[5]				14
2017	[5]				(3)
2018	[5]				3
2019	[5]				(3)
2020	[5]				(3)
2021	[5]				$ 0
Commonwealth Edison Co [Member] | Intangible Asset Two Thousand Three Chicago Settlement Agreement [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[6]				17 years 10 months 24 days
Gross	[6]				$ 62
Accumulated Amortization	[6]				(47)
Net	[6]				15
2017	[6]				(4)
2018	[6]				4
2019	[6]				(4)
2020	[6]				(4)
2021	[6]				$ 0
Pepco Holdings LLC [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period					6 years 9 months 18 days
Gross					$ (1,515)
Accumulated Amortization					430
Net					(1,085)
2017					(335)
2018					(189)
2019					119
2020					(115)
2021					(92)
Pepco Holdings LLC [Member] | Utility Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Gross					25
Accumulated Amortization					0
Net					25
2017					0
2018					0
2019					0
2020					0
2021					0
Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
2017					(9)
2018					(7)
2019					(6)
2020					2
2021					$ 4
Exelon Wind Acquisition [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Wind turbine supply megawatt | MW			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	[2],[7],[8]				18 years
Gross	[7],[8]				$ 224
Accumulated Amortization	[7],[8]				(83)
Net	[7],[8]				141
2017	[7],[8]				(14)
2018	[7],[8]				14
2019	[7],[8]				(14)
2020	[7],[8]				(10)
2021	[7],[8]				$ 10
Antelope Valley Acquisition [Member] | Exelon Generation Co L L C [Member]
Finite-Lived Intangible Assets [Line Items]
Wind turbine supply megawatt | MW		242
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	[2],[8],[9]				25 years
Gross	[8],[9]				$ 190
Accumulated Amortization	[8],[9]				(28)
Net	[8],[9]				162
2017	[8],[9]				(8)
2018	[8],[9]				8
2019	[8],[9]				(8)
2020	[8],[9]				(8)
2021	[8],[9]				$ 8
Constellation Energy Group LLC [Member] | Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[4],[8]				1 year 6 months
Gross	[4],[8]				$ 1,499
Accumulated Amortization	[4],[8]				(1,440)
Net	[4],[8]				59
2017	[4],[8]				(21)
2018	[4],[8]				(11)
2019	[4],[8]				(8)
2020	[4],[8]				(10)
2021	[4],[8]				$ 10
Constellation Energy Group LLC [Member] | Exelon Generation Co L L C [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[3],[4]				12 years 4 months 24 days
Gross	[3],[4]				$ 214
Accumulated Amortization	[3],[4]				(94)
Net	[3],[4]				120
2017	[3],[4]				(18)
2018	[3],[4]				18
2019	[3],[4]				(17)
2020	[3],[4]				(17)
2021	[3],[4]				$ 17
Constellation Energy Group LLC [Member] | Exelon Generation Co L L C [Member] | Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[4]				10 years
Gross	[4]				$ 243
Accumulated Amortization	[4]				(125)
Net	[4]				118
2017	[4]				(23)
2018	[4]				23
2019	[4]				(23)
2020	[4]				(23)
2021	[4]				$ 23
CENG [Member] | Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[8],[10]				1 year 8 months 12 days
Gross	[8],[10]				$ (97)
Accumulated Amortization	[8],[10]				59
Net	[8],[10]				(38)
2017	[8],[10]				(15)
2018	[8],[10]				18
2019	[8],[10]				(15)
2020	[8],[10]				(8)
2021	[8],[10]				$ 4
Integrys [Member] | Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[8],[10]				2 years 4 months 24 days
Gross	[8],[11]				$ 5
Accumulated Amortization	[8],[11]				(3)
Net	[8],[11]				2
2017	[8],[11]				(1)
2018	[8],[11]				1
2019	[8],[11]				0
2020	[8],[11]				0
2021	[8],[11]				$ 0
Integrys [Member] | Exelon Generation Co L L C [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[3],[11]				10 years
Gross	[3],[11]				$ 50
Accumulated Amortization	[3],[11]				(11)
Net	[3],[11]				39
2017	[3],[11]				(5)
2018	[3],[11]				5
2019	[3],[11]				(5)
2020	[3],[11]				(5)
2021	[3],[11]				$ 5
PES [Member] | Exelon Generation Co L L C [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period					15 years
Gross					$ 12
Accumulated Amortization					(1)
Net	[3],[11]				11
2017					(1)
2018					1
2019					(1)
2020					(1)
2021					$ 1
PES [Member] | Exelon Generation Co L L C [Member] | Customer Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[4]				1 year
Gross	[4]				$ 9
Accumulated Amortization	[4]				(7)
Net	[4]				2
2017	[4]				(2)
2018	[4]				0
2019	[4]				0
2020	[4]				0
2021	[4]				$ 0
ConEdison Solutions [Member] | Exelon Generation Co L L C [Member] | Unamortized Energy Contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period					1 year 6 months
Gross	[8],[11]				$ 100
Accumulated Amortization					(53)
Net	[8],[11]				47
2017					(37)
2018					7
2019					(2)
2020					$ (1)
ConEdison Solutions [Member] | Exelon Generation Co L L C [Member] | Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average amortization period	[2],[3],[11]				10 years
Gross	[3],[11]				$ 9
Accumulated Amortization	[3],[11]				0
Net	[3],[11]				9
2017	[3],[11]				(1)
2018	[3],[11]				1
2019	[3],[11]				(1)
2020	[3],[11]				(1)
2021	[3],[11]				$ 1

[1] (a)On May 31, 2015, Exelon entered into a long-term software license agreement. Exelon is required to make payments starting August 2015 through May 2024. The intangible asset recognized as a result of these payments is being amortized on a straight-line basis over the contract term.

[2] Weighted-average amortization period was calculated at the date of a) acquisition for acquired assets or b) settlement agreement.

[3] Excludes $11 million of other miscellaneous customer relationships that have been acquired. The estimated amortization for these miscellaneous customer relationships is $1 million in each of the years from 2017 to 2021.

[4] On March 12, 2012, Constellation merged into Exelon with Exelon continuing as the surviving corporation pursuant to the transactions contemplated by the Agreement and Plan of Merger. Since the merger transaction, Generation includes the former Constellation generation and customer supply operations.

[5] 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.

[6] In February 2003, ComEd entered into separate agreements with the City of Chicago and with Midwest Generation, LLC (Midwest Generation). Under the terms of the settlement agreement with the City of Chicago, ComEd agreed to pay the City of Chicago a total of $60 million over a ten-year period, beginning in 2003. The intangible asset recognized as a result of the settlement agreement is being amortized ratably over the remaining term of the City of Chicago franchise agreement, which ends in 2020. As required by the settlement, ComEd also made a payment of $2 million to a third-party on the City of Chicago’s behalf. Under the terms of the agreement with Midwest Generation, ComEd received payments of $32 million from Midwest Generation to relieve Midwest Generation’s obligation under the 1999 fossil sale agreement with ComEd to build the generation facility in the City of Chicago. The payments received by ComEd, which have been recorded in Other deferred credits and other liabilities, and other long-term liabilities on Exelon's and ComEd's Consolidated Balance Sheets are being recognized ratably (approximately $2 million annually) as an offset to amortization expense over the remaining term of the franchise agreement.

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

[8] Includes unamortized energy contract assets and liabilities on Exelon's and Generation's Consolidated Balance Sheets. Excludes $10 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 $(9) million, $(7) million, $(6) million, $(2) million and $4 million for 2017, 2018, 2019, 2020 and 2021, respectively.

[9] In September 2011, Generation acquired all of the interest in Antelope Valley Solar Ranch One, a 242 MW solar project in northern Los Angeles County, CA from First Solar, Inc.

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

[11] See Note 4—Mergers, Acquisitions, and Dispositions for additional information.