Derivative Financial Instruments (Fair Value Measurments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended						6 Months Ended		9 Months Ended				12 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Jun. 30, 2012		Jun. 30, 2013		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012		Dec. 31, 2011
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Ineffective portion recognized in income									$ 1
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Net gain (loss) of reclassifications from accumulated OCI to net income related to settlements of block contracts											0
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	730								730				938
Mark-to-market derivative assets (noncurrent assets)	779								779				937
Mark-to-market derivative liabilities (current liabilities)	(126)								(126)				(352)
Mark-to-market derivative liabilities (noncurrent liabilities)	(218)								(218)				(281)
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	180		(91)						217		98
Reclassification to realized at settlement	66		123						61		216
Net mark-to-market gains (losses)	246		32						278		314
Operating Revenue [Member]
Proprietary Trading Activities [Abstract]
Change in fair value	0		(2)						1		12
Reclassification to realized at settlement	(40)		25						(36)		57
Net mark-to-market gains (losses)	(40)		23						(35)		69
Derivative [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	728								728				934
Mark-to-market derivative assets (noncurrent assets)	733								733				878
Total mark-to-market derivative assets	1,461								1,461				1,812
Mark-to-market derivative liabilities (current liabilities)	(124)								(124)				(350)
Mark-to-market derivative liabilities (noncurrent liabilities)	(204)								(204)				(250)
Total mark-to-market derivative liabilities	(328)								(328)				(600)
Total mark-to-market derivative net assets (liabilities)	1,133								1,133				1,212
Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedge reclassified from AOCI to net income
Cash Flow Hedge Activity Impact [Abstract]
Cash flow hedge activity impact on pre-tax net income based on reclassification adjustment from accumulated other comprehensive income	84		145						324		548
Total Cash Flow Hedges [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Accumulated OCI derivative gain - Beginning Balance	245		547				368		368		488		488
Effective portion of changes in fair value	2	[1]	0	[2]					25	[3]	301	[4]
Accumulated OCI derivative gain - Ending Balance	199		459						199		459
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Net gains (losses) related to interest rate swaps and treasury rate locks											(22)
Net gain (loss) related to effective portion of changes in fair value of treasury rate locks	2		0						(25)
Total Cash Flow Hedges [Member] | Operating Revenue [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Ineffective portion recognized in income											3
Total Cash Flow Hedges [Member] | Operating Revenue [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedge reclassified from AOCI to net income
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Reclassifications from accumulated OCI to net income	(48)		(88)						(194)		(333)
Exelon Generation Co L L C [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Reclassifications from accumulated OCI to net income	3,871		3,558						10,729		9,276
Cash Flow Hedge Activity Impact [Abstract]
Net unrealized pre-tax gain (loss) on effective cash flow hedges									1,928
Net unrealized pre-tax gain (loss) on effective cash flow hedges related to swap contract									693
Expected reclassification from accumulated other comprehensive income to results of operations									271
Expected reclassification from accumulated other comprehensive income to results of operations related to fair value of swap contracts									0
Cash flow hedge activity impact on pre-tax net income based on reclassification adjustment from accumulated other comprehensive income	84		283						543		1,005
Change in cash flow hedge ineffectiveness									0		5
Cash flow hedge ineffectiveness adjustment to accumulated other comprehensive income			5								5
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	730								730				938
Mark-to-market derivative assets with affiliate (current assets)	0								0				226
Mark-to-market derivative assets (noncurrent assets)	766								766				924
Mark-to-market derivative liabilities (current liabilities)	(110)								(110)				(334)
Mark-to-market derivative liabilities (noncurrent liabilities)	(112)								(112)				(232)
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	180		(126)						223		36
Reclassification to realized at settlement	66		142						48		245
Net mark-to-market gains (losses)	246		16						271		281
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Proprietary Trading Activities [Abstract]
Change in fair value	0		(2)						1		12
Reclassification to realized at settlement	(40)		25						(36)		57
Net mark-to-market gains (losses)	(40)		23						(35)		69
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	175		(255)						149		(85)
Reclassification to realized at settlement	41		20						(15)		(81)
Net mark-to-market gains (losses)	216		(235)						134		(166)
Exelon Generation Co L L C [Member] | Operating Revenue [Member] | Consolidation, Eliminations [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	0		35						(6)		62
Reclassification to realized at settlement	0		(19)						13		(29)
Net mark-to-market gains (losses)	0		16						7		33
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	5		129						74		121
Reclassification to realized at settlement	25		122						63		326
Net mark-to-market gains (losses)	30		251						137		447
Exelon Generation Co L L C [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	728	[5]							728	[5]			934	[6]
Mark-to-market derivative assets with affiliate (current assets)													226	[6]
Mark-to-market derivative assets (noncurrent assets)	733	[5]							733	[5]			878	[6]
Total mark-to-market derivative assets	1,461	[5]							1,461	[5]			2,038	[6]
Mark-to-market derivative liabilities (current liabilities)	(108)	[5]							(108)	[5]			(332)	[6]
Mark-to-market derivative liabilities (noncurrent liabilities)	(98)	[5]							(98)	[5]			(201)	[6]
Total mark-to-market derivative liabilities	(206)	[5]							(206)	[5]			(533)	[6]
Total mark-to-market derivative net assets (liabilities)	1,255	[5]							1,255	[5]			1,505	[6]
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	2,244								2,244				2,883	[7]
Mark-to-market derivative assets with affiliate (current assets)													226	[7]
Mark-to-market derivative assets (noncurrent assets)	1,540								1,540				1,792	[7]
Total mark-to-market derivative assets	3,784								3,784				4,901	[7]
Mark-to-market derivative liabilities (current liabilities)	(1,812)								(1,812)				(2,419)	[7]
Mark-to-market derivative liabilities (noncurrent liabilities)	(911)								(911)				(1,080)	[7]
Total mark-to-market derivative liabilities	(2,723)								(2,723)				(3,499)	[7]
Total mark-to-market derivative net assets (liabilities)	1,061								1,061				1,402	[7]
Footnotes To Derivative Instruments In Statement Of Financial Position Fair Value [Abstract]
Current assets collateral offset	86								86				113
Noncurrent assets collateral offset	8								8				201
Current liabilities collateral offset	(235)								(235)				(214)
Noncurrent liabilities collateral offset	(5)								(5)				(131)
Total cash collateral received net of cash collateral posted													31
Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member]
Footnotes To Derivative Instruments In Statement Of Financial Position Fair Value [Abstract]
Fair value swap contract current asset	0								0				226
Fair value swap contract noncurrent asset													0
Noncurrent liability DOE interest rate swap									23				0
Exelon Generation Co L L C [Member] | Proprietary Trading [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	1,577								1,577				2,469
Mark-to-market derivative assets (noncurrent assets)	447								447				724
Total mark-to-market derivative assets	2,024								2,024				3,193
Mark-to-market derivative liabilities (current liabilities)	(1,538)								(1,538)				(2,432)
Mark-to-market derivative liabilities (noncurrent liabilities)	(438)								(438)				(689)
Total mark-to-market derivative liabilities	(1,976)								(1,976)				(3,121)
Total mark-to-market derivative net assets (liabilities)	48								48				72
Exelon Generation Co L L C [Member] | Collateral And Netting [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	(3,093)	[8]							(3,093)	[8]			(4,418)	[8]
Mark-to-market derivative assets (noncurrent assets)	(1,254)	[8]							(1,254)	[8]			(1,638)	[8]
Total mark-to-market derivative assets	(4,347)	[8]							(4,347)	[8]			(6,056)	[8]
Mark-to-market derivative liabilities (current liabilities)	3,242	[8]							3,242	[8]			4,519	[8]
Mark-to-market derivative liabilities (noncurrent liabilities)	1,251	[8]							1,251	[8]			1,568	[8]
Total mark-to-market derivative liabilities	4,493	[8]							4,493	[8]			6,087	[8]
Total mark-to-market derivative net assets (liabilities)	146	[8]							146	[8]			31	[8]
Footnotes To Derivative Instruments In Statement Of Financial Position Fair Value [Abstract]
Total cash collateral received net of cash collateral posted	146								146
Exelon Generation Co L L C [Member] | Energy Related Hedges [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Accumulated OCI derivative gain - Beginning Balance	255	[9]	923	[10],[11]			532	[12]	532	[12]	925	[13],[14]	925	[13],[14]
Effective portion of changes in fair value			0	[15]							432	[16]
Accumulated OCI derivative gain - Ending Balance	204	[12],[9]	752	[10],[11],[13],[14]	923	[10],[11]	255	[9]	204	[12],[9]	752	[10],[11],[13],[14]	532	[12]	925	[13],[14]
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Unrealized gain (loss) related to fair value of swap contract			232		315						232		0		420
Unrealized gain (loss) related to fair value of block contract			0								0				0
Net gain (loss) related to effective portion of changes in fair value of swap contract									0				133
Net gain (loss) of reclassifications from accumulated OCI to net income related to the settlements of swap contract			(83)
Net gains (losses) related to interest rate swaps and treasury rate locks	(11)		(22)		22		(11)		(11)				(20)		(10)
Net gain (loss) related to effective portion of changes in fair value of treasury rate locks											88
Exelon Generation Co L L C [Member] | Energy Related Hedges [Member] | Operating Revenue [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Ineffective portion recognized in income											3
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Net gain (loss) of reclassifications from accumulated OCI to net income related to the settlements of swap contract	0								(133)		(276)
Exelon Generation Co L L C [Member] | Energy Related Hedges [Member] | Operating Revenue [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Cash Flow Hedge reclassified from AOCI to net income
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Reclassifications from accumulated OCI to net income	(51)		(171)						(328)	[17]	(608)
Commonwealth Edison Co [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative liabilities (current liabilities)	(16)								(16)				(18)
Mark-to-market derivative liability with affiliate (current liability)	0								0				(226)
Mark-to-market derivative liabilities (noncurrent liabilities)	(106)								(106)				(49)
Commonwealth Edison Co [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative liabilities (current liabilities)													(18)	[7]
Mark-to-market derivative liability with affiliate (current liability)													(226)	[7]
Mark-to-market derivative liabilities (noncurrent liabilities)													(49)	[7]
Total mark-to-market derivative liabilities													(293)	[7]
Total mark-to-market derivative net assets (liabilities)													(293)	[7]
Commonwealth Edison Co [Member] | Designated as Hedging Instrument [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative liabilities (current liabilities)	(16)	[18]							(16)	[18]
Mark-to-market derivative liabilities (noncurrent liabilities)	(106)	[18]							(106)	[18]
Total mark-to-market derivative liabilities	(122)	[18]							(122)	[18]
Total mark-to-market derivative net assets (liabilities)	(122)	[18]							(122)	[18]
Commonwealth Edison Co [Member] | Cash Flow Hedging [Member]
Footnotes To Derivative Instruments In Statement Of Financial Position Fair Value [Abstract]
Fair value swap contract current liability	0								0				226
Fair value swap contract noncurrent liability													0
Commonwealth Edison Co [Member] | Intersegment Eliminations [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets with affiliate (current assets)													(226)	[7]
Total mark-to-market derivative assets													(226)	[7]
Mark-to-market derivative liability with affiliate (current liability)													226	[7]
Total mark-to-market derivative liabilities													226	[7]
Baltimore Gas and Electric Company [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Reclassifications from accumulated OCI to net income	$ 735		$ 716						$ 2,261		$ 2,023

[1] (b)         Includes $2 million of gains, net of taxes, related to the effective portion of changes in fair value of interest rate swaps and treasury rate locks.

[2] Includes $0 million of losses, net of taxes, at Generation related to the effective portion of changes in fair value of interest rate swaps and treasury rate locks.

[3] Includes $25 million of losses, net of taxes, related to the effective portion of changes in fair value of interest rate swaps and treasury rate locks.

[4] Includes $12 million of losses, net of taxes, related to the effective portion of changes in fair value of interest rate swaps and treasury rate locks.

[5] Current and noncurrent assets are shown net of collateral of $86 million and $8 million, respectively, and current and noncurrent liabilities are shown net of collateral of $(235) million and $(5) million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $146 million at September 30, 2013.

[6] (c)        Current and noncurrent assets are shown net of collateral of $113 million and $201 million, respectively, and current and noncurrent liabilities are shown net of collateral of $ (214) million and $ (131) million, respectively. The total cash collateral received, net of cash collateral posted and offset against mark-to-market assets and liabilities was $31 million at December 31, 2012.

[7] (a)        Includes current and noncurrent assets for Generation and current and noncurrent liabilities for ComEd of $226 million related to the fair value of the five-year financial swap contract between Generation and ComEd, as described above. For Generation excludes $28 million of noncurrent liability relating to an interest rate swap in connection with a loan agreement to fund Antelope Valley as discussed above.

[8] Exelon and Generation net all available amounts allowed under the derivative accounting guidance on the balance sheet. These amounts include unrealized derivative transactions with the same counterparty under legally enforceable master netting agreements and cash collateral.  In some cases Exelon and Generation may have other offsetting exposures, subject to a master netting or similar agreement, such as trade receivables and payables, transactions that do not qualify as derivatives, letters of credit and other forms of non-cash collateral. These are not reflected in the table above.

[9] Excludes $11 million of losses, net of taxes, related to interest rate swaps and treasury rate locks as of September 30, 2013 and June 30, 2013.

[10] Includes $232 million and $315 million of gains, net of taxes, related to the fair value of the five-year financial swap contract with ComEd as of September 30, 2012 and June 30, 2012, respectively.

[11] Excludes $22 million of losses and $22 million of gains, net of taxes, related to interest rate swaps and treasury rate locks for the three months ended September 30, 2012 and June 30, 2012 respectively.

[12] Excludes $11 million of losses and $20 million of losses, net of taxes, related to interest rate swaps and treasury locks as of September 30, 2013 and December 31, 2012, respectively.

[13] Includes $232 million and $420 million of gains, net of taxes, related to the fair value of the five-year financial swap contract with ComEd, as of September 30, 2012 and December 31, 2011.

[14] Excludes $22 million of losses and $10 million of losses, net of taxes, related to interest rate swaps and treasury rate locks for the nine months ended September 30, 2012 and year ended December 31, 2011, respectively.

[15] Includes $2 million of gains, net of taxes, related to the effective portion of changes in fair value of interest rate swaps and treasury rate locks.

[16] Includes $88 million of gains, net of taxes, related to the effective portion of changes in fair value of the five-year financial swap contract with ComEd through the date of de-designation prior to the merger.

[17]         Includes $133 million of gains, net of taxes, related to the fair value of the five-year financial swap contract with ComEd, as of December 31, 2012.

[18] Includes current and noncurrent liabilities relating to floating-to-fixed energy swap contracts with unaffiliated suppliers.