Merger and Acquisitions (Details) (USD $)	3 Months Ended								12 Months Ended								3 Months Ended								12 Months Ended											12 Months Ended									12 Months Ended			12 Months Ended
	Dec. 31, 2011 MW	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011 MW		Dec. 31, 2010		Dec. 31, 2009		Dec. 31, 2011 Constellation Energy Group Acquisition [Member] MW	Dec. 31, 2011 Wolf Hollow Acquisition [Member] MW	Dec. 31, 2011 Exelon Generation Co L L C [Member]	Sep. 30, 2011 Exelon Generation Co L L C [Member]	Jun. 30, 2011 Exelon Generation Co L L C [Member]	Mar. 31, 2011 Exelon Generation Co L L C [Member]	Dec. 31, 2010 Exelon Generation Co L L C [Member]	Sep. 30, 2010 Exelon Generation Co L L C [Member]	Jun. 30, 2010 Exelon Generation Co L L C [Member]	Mar. 31, 2010 Exelon Generation Co L L C [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member]		Dec. 31, 2010 Exelon Generation Co L L C [Member]		Dec. 31, 2009 Exelon Generation Co L L C [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] Exelon Wind Acquisition [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] Antelope Valley Acquisition [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] John Deere Renewables Acquisition [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Wolf Hollow Acquisition [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] Antelope Valley Solar Ranch One Acquisition [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] John Deere Renewables Acquisition [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Wolf Hollow Acquisition [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Antelope Valley Solar Ranch One Acquisition [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Other Development Projects [Member]		Dec. 31, 2011 Exelon Generation Co L L C [Member] John Deere Renewables Acquisition [Member] MW	Dec. 31, 2011 Exelon Generation Co L L C [Member] Wolf Hollow Acquisition [Member]	Aug. 24, 2011 Exelon Generation Co L L C [Member] Wolf Hollow Acquisition [Member]	Dec. 31, 2011 Exelon Generation Co L L C [Member] Antelope Valley Solar Ranch One Acquisition [Member] MW
Standard acquisition information [Abstract]
Purchase Price															$ 7,900,000,000
Transaction Costs																																														4,000,000		8,000,000
Plant Acquisition Watts	104								104							720																													735			230
Contingent consideration potential cash payment																																													40,000,000
Contingent consideration at fair value																																													32,000,000
Contingent consideration paid																																													16,000,000
Acquired customer receivables																																													18,000,000
Value of noncontrolling interest																																													3,000,000
Acquisition-related costs																																														4,000,000		8,000,000
Revenues	3,991,000,000	5,295,000,000	4,587,000,000	5,052,000,000	4,494,000,000	5,291,000,000	4,398,000,000	4,461,000,000	18,924,000,000	[1]	18,644,000,000	[1]	17,318,000,000	[1]			2,161,000,000	2,862,000,000	2,546,000,000	2,739,000,000	2,596,000,000	2,655,000,000	2,353,000,000	2,421,000,000	10,308,000,000	[1]	10,025,000,000	[1]	9,703,000,000	[1]																30,000,000
Operating Income (Loss)	1,062,000,000	1,181,000,000	1,034,000,000	1,202,000,000	939,000,000	1,367,000,000	1,018,000,000	1,402,000,000	4,480,000,000		4,726,000,000		4,750,000,000				673,000,000	754,000,000	647,000,000	801,000,000	660,000,000	883,000,000	587,000,000	916,000,000	2,876,000,000		3,046,000,000		3,295,000,000																	(5,000,000)
Intangible assets assumed																																													224,000,000			190,000,000
Intangible assets related to PPAs																																													48,000,000
First Solar Corporation Payable																																																135,000,000
Gain Loss On Purchase Power Agreement Settlement																																														6,000,000
Business Combination, Bargain Purchase, Gain (Loss) Recognized, Amount																																														36,000,000
Intangible asset amortization expense																																													9,000,000
Contingent Consideration Included in Escrow	4,000,000								4,000,000
CEG Business Acquisition [Abstract]
CEG Plant Divestiture Wattage															2,648
CEG merger integration costs															77,000,000
Proposed direct merger investment to state									1,000,000,000						1,000,000,000
Termination costs from acquirer to acquiree															800,000,000
Termination costs from acquiree to Exelon															200,000,000
Antelope Business Acquisition [Abstract]
Expected investment in equity in projects	148,000,000								148,000,000																																							713,000,000
DOE loan guarantee									646,000,000																																							646,000,000
DOE advances received																																																66,000,000
DOE interest rate swap									485,000,000																																							485,000,000
Percentage of interest rate swap in relation to DOE guarantee																	0.75								0.75																							0.75
Plant Acquisition [Abstract]
Fair value of receivables for insurance claims																																														4,000,000	14,000,000
Acquisition of Exelon Wind [Abstract]
Acquisition of John Deere Renewables additional wind projects in advance stages of development capacity																																													230
Probability of project to be constructed																																													100
Contingent consideration recorded in operation and maintenance expense																																													2,000,000
Contingent consideration recorded in current liabilities																																													10,000,000
Contingent consideration recorded in deferred credits																																													8,000,000
Fair Value Of Consideration Transferred [Abstract]
Cash																																								893,000,000	311,000,000	75,000,000	3,000,000
Contingent consideration at fair value					(32,000,000)						(32,000,000)										(32,000,000)						(32,000,000)													32,000,000			(9,000,000)	[2]
Gain on purchase power agreement settlement																																									(6,000,000)
Total fair value of consideration recorded																																								925,000,000	305,000,000	75,000,000	12,000,000
Recognized Amounts Of Identifiable Assets Acquired And Liabilities Assumed [Abstract]
Property, plant and equipment	12,000,000								12,000,000																										700,000,000	347,000,000		15,000,000	[3]
Inventory																																				5,000,000
Payable to First Solar acquisition																																						(135,000,000)
Intangible assets																																			224,000,000			190,000,000	[4]
Working capital																																			18,000,000	(5,000,000)	[5]
Asset retirement obligation																																			(13,000,000)
Noncontrolling interest																																			(3,000,000)
Other																																			(1,000,000)			5,000,000
Total net identifiable assets	12,000,000								12,000,000																										925,000,000	347,000,000		75,000,000
Business combination, bargain purchase, gain recognized, amount																																				(42,000,000)
Footnotes To Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Net [Abstract]
Amount of long-term debt																						350,000,000
Finite Lived Intangible Assets Future Amortization Expense [Abstract]
Future Amortization Expense Year One									20,000,000																						13,000,000	[6]	0	[7]
Future Amortization Expense Year Two									27,000,000																						14,000,000	[6]	6,000,000	[7]
Future Amortization Expense Year Three									28,000,000																						14,000,000	[6]	7,000,000	[7]
Future Amortization Expense Year Four									28,000,000																						14,000,000	[6]	7,000,000	[7]
Future Amortization Expense Year Five									28,000,000																						14,000,000	[6]	7,000,000	[7]
Finite Lived Intangible Assets Net [Abstract]
Finite lived intangible assets gross	576,000,000								576,000,000																						224,000,000	[6]	190,000,000	[7]
Finite lived intangible assets accumulated amortization	(113,000,000)								(113,000,000)																						(13,000,000)	[6]	0	[7]
Finite lived intangible assets net	463,000,000								463,000,000																						211,000,000	[6]	190,000,000	[7]
Finite Lived Intangible Assets Amortization Expense [Abstract]
Intangible asset amortization expense									19,000,000		8,000,000		7,000,000												12,000,000		1,000,000		0
John Deere Renewables [Abstract]
PPA's for projects in advanced stages of development																	$ 21,000,000								$ 21,000,000

[1] Includes operating revenues from affiliates.

[2] For the Shooting Star acquisition, the balance includes $4 million of cash placed in escrow which will be paid to Infinity Wind Holdings, LLC upon commencement of construction.

[3] Generation concluded that the remaining, yet-to-be paid $135 million in consideration was embedded in the amounts payable under the Engineering, Procurement, Construction (EPC) agreement for First Solar, Inc. to construct the solar facility. For accounting purposes, this aspect of the transaction is considered to be akin to a "seller financing" arrangement. As such, Generation recorded a liability of $135 million associated with the portion of the future payments to First Solar, Inc. under the EPC agreement to reflect Generation's implicit amounts due First Solar, Inc. for the remainder of the value of the net assets acquired. The $135 million payable to First Solar, Inc. will be relieved as Generation makes payments for costs incurred over the project construction period.

[4] See Note 7 - Intangible Assets for additional information.

[5] Working capital acquired for Wolf Hollow is subject to a 180-day adjustment period.

[6] Refer to Note 3 - Acquisition for additional information regarding Exelon Wind.

[7] Refer to Note 3 - Acquisition for additional information regarding Antelope Valley.