Derivative Financial Instruments (Fair Value Measurments) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	$ 727		$ 938
Mark-to-market derivative assets (noncurrent assets)	607		937
Mark-to-market derivative liabilities (current liabilities)	(159)		(352)
Mark-to-market derivative liabilities (noncurrent liabilities)	(300)		(281)
Total mark-to-market derivative net assets (liabilities)	854
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	459		(241)
Reclassification to realized at settlement	52		768
Net mark-to-market gains (losses)	511		527
Operating Revenue [Member] | Intersegment Eliminations [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	(6)	[1]	(94)	[1]
Reclassification to realized at settlement	13	[1]	101	[1]
Net mark-to-market gains (losses)	7	[1]	7	[1]
Derivative [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets			934
Mark-to-market derivative assets with affiliate (current assets)	728
Mark-to-market derivative assets (noncurrent assets)	569		878
Total mark-to-market derivative assets	1,297		1,812
Mark-to-market derivative liabilities (current liabilities)	(158)		(350)
Mark-to-market derivative liabilities (noncurrent liabilities)	(285)		(250)
Total mark-to-market derivative liabilities	(443)		(600)
Total mark-to-market derivative net assets (liabilities)			1,212
Energy Related Hedges [Member] | Operating Revenue One [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
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	464		747		512
Total Cash Flow Hedges [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Accumulated OCI derivative gain - Beginning Balance	368		488
Effective portion of changes in fair value	29	[2]	330	[2]
Accumulated OCI derivative gain - Ending Balance	120		368		488
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	464		747		512
Total Cash Flow Hedges [Member] | Operating Revenue One [Member]
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	0		10		1
Total Cash Flow Hedges [Member] | Operating Revenue One [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	(277)		(453)
Total Cash Flow Hedges [Member] | Purchased PowerOne [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Ineffective portion recognized in income			3
Exelon Generation Co L L C [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Reclassifications from accumulated OCI to net income	14,207		12,735		9,286
Cash Flow Hedge Activity Impact [Abstract]
Expected reclassification from accumulated other comprehensive income to results of operations	195
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	727		938
Mark-to-market derivative assets with affiliate (current assets)			226
Mark-to-market derivative assets (noncurrent assets)	600		924
Mark-to-market derivative liabilities (current liabilities)	(142)		(334)
Mark-to-market derivative liabilities (noncurrent liabilities)	(120)		(232)
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	465		(147)		218
Reclassification to realized at settlement	39		667		(515)
Net mark-to-market gains (losses)	504		520		(297)	[3]
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Proprietary Trading Activities [Abstract]
Change in fair value	(21)		(12)		23
Reclassification to realized at settlement	(18)		108		(26)
Net mark-to-market gains (losses)	(39)		96		(3)
Exelon Generation Co L L C [Member] | Pro Forma [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value					218
Reclassification to realized at settlement					(515)
Net mark-to-market gains (losses)					(297)	[3]
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	285		(362)		87
Reclassification to realized at settlement	(65)		429		(296)
Net mark-to-market gains (losses)	220		67		(209)	[3]
Exelon Generation Co L L C [Member] | Operating Revenue [Member] | Pro Forma [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value					258
Reclassification to realized at settlement					(516)
Net mark-to-market gains (losses)					(258)	[3]
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	180		215		131
Reclassification to realized at settlement	104		238		(219)
Net mark-to-market gains (losses)	284		453		(88)	[3]
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member] | Pro Forma [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value					(40)
Reclassification to realized at settlement					1
Net mark-to-market gains (losses)					(39)	[3]
Exelon Generation Co L L C [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets			934	[4]
Mark-to-market derivative assets with affiliate (current assets)	728	[5]	226	[4]
Mark-to-market derivative assets (noncurrent assets)	569	[5]	878	[4]
Total mark-to-market derivative assets	1,297	[5]	2,038	[4]
Mark-to-market derivative liabilities (current liabilities)	(141)	[5]	(332)	[4]
Mark-to-market derivative liabilities (noncurrent liabilities)	(109)	[5]	(201)	[4]
Total mark-to-market derivative liabilities	(250)	[5]	(533)	[4]
Total mark-to-market derivative net assets (liabilities)	1,047	[5]	1,505	[4]
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	2,616		2,883	[6]
Mark-to-market derivative assets with affiliate (current assets)			226	[6]
Mark-to-market derivative assets (noncurrent assets)	1,344		1,792	[6]
Total mark-to-market derivative assets	3,960		4,901	[6]
Mark-to-market derivative liabilities (current liabilities)	(2,023)		(2,419)	[6]
Mark-to-market derivative liabilities (noncurrent liabilities)	(804)		(1,080)	[6]
Total mark-to-market derivative liabilities	(2,827)		(3,499)	[6]
Total mark-to-market derivative net assets (liabilities)	1,133		1,402	[6]
Footnotes To Derivative Instruments In Statement Of Financial Position Fair Value [Abstract]
Current assets collateral offset	84		113
Noncurrent assets collateral offset	72		201
Current liabilities collateral offset	(12)		(214)
Noncurrent liabilities collateral offset	0		(131)
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		226
Fair value swap contract noncurrent asset			0
Noncurrent liability DOE interest rate swap			28
Exelon Generation Co L L C [Member] | Proprietary Trading [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	1,476		2,469
Mark-to-market derivative assets (noncurrent assets)	285		724
Total mark-to-market derivative assets	1,761		3,193
Mark-to-market derivative liabilities (current liabilities)	(1,410)		(2,432)
Mark-to-market derivative liabilities (noncurrent liabilities)	(293)		(689)
Total mark-to-market derivative liabilities	(1,703)		(3,121)
Total mark-to-market derivative net assets (liabilities)	58		72
Exelon Generation Co L L C [Member] | Collateral And Netting [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	(3,364)	[7]	(4,418)	[7]
Mark-to-market derivative assets (noncurrent assets)	(1,060)	[7]	(1,638)	[7]
Total mark-to-market derivative assets	(4,424)	[7]	(6,056)	[7]
Mark-to-market derivative liabilities (current liabilities)	3,292	[7]	4,519	[7]
Mark-to-market derivative liabilities (noncurrent liabilities)	988	[7]	1,568	[7]
Total mark-to-market derivative liabilities	4,280	[7]	6,087	[7]
Total mark-to-market derivative net assets (liabilities)	(144)	[7]	31	[7]
Footnotes To Derivative Instruments In Statement Of Financial Position Fair Value [Abstract]
Total cash collateral received net of cash collateral posted	144		(31)
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	532	[8],[9]	925	[8],[9]
Effective portion of changes in fair value	0		432	[10]
Accumulated OCI derivative gain - Ending Balance	119	[9]	532	[8],[9]
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Net gain (loss) related to effective portion of changes in fair value of swap contract			88
Exelon Generation Co L L C [Member] | Energy Related Hedges [Member] | Operating Revenue One [Member]
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Unrealized gain (loss) related to fair value of swap contract			133		420
Net gain (loss) of reclassifications from accumulated OCI to net income related to the settlements of swap contract	133		375
Exelon Generation Co L L C [Member] | Energy Related Hedges [Member] | Operating Revenue One [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	(413)	[11]	(828)	[11]
Exelon Generation Co L L C [Member] | Energy Related Hedges [Member] | Purchased PowerOne [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Ineffective portion recognized in income			3
Exelon Generation Co L L C [Member] | Total Cash Flow Hedges [Member]
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Net gains (losses) related to interest rate swaps and treasury rate locks	(5)		(20)
Net gain (loss) related to effective portion of changes in fair value of treasury rate locks	(15)		(9)
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	683		1,368		968
Exelon Generation Co L L C [Member] | Total Cash Flow Hedges [Member] | Operating Revenue One [Member]
Cash Flow Hedge Activity Impact [Abstract]
Net unrealized pre-tax gain (loss) on effective cash flow hedges	0		5		10
Commonwealth Edison Co [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets (noncurrent assets)	0		0
Mark-to-market derivative liabilities (current liabilities)	(17)		(18)
Mark-to-market derivative liability with affiliate (current liability)	0		(226)
Mark-to-market derivative liabilities (noncurrent liabilities)	(176)		(49)
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)	0		0
Commonwealth Edison Co [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Total mark-to-market derivative net assets (liabilities)	(193)	[12]
Commonwealth Edison Co [Member] | Derivative [Member] | Intersegment Eliminations [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets with affiliate (current assets)			(226)	[6]
Total mark-to-market derivative assets			(226)	[6]
Mark-to-market derivative liability with affiliate (current liability)			226	[6]
Total mark-to-market derivative liabilities			226	[6]
Commonwealth Edison Co [Member] | Designated as Hedging Instrument [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative liabilities (current liabilities)	(17)	[12]	(18)	[12],[6]
Mark-to-market derivative liability with affiliate (current liability)			(226)	[12],[6]
Mark-to-market derivative liabilities (noncurrent liabilities)	(176)	[12]	(49)	[12],[6]
Total mark-to-market derivative liabilities	(193)	[12]	(293)	[12],[6]
Total mark-to-market derivative net assets (liabilities)			(293)	[12],[6]
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		226
Fair value swap contract noncurrent liability			0
PECO Energy Co [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative liabilities (current liabilities)	0		0
Mark-to-market derivative liability with affiliate (current liability)	0		0
Mark-to-market derivative liabilities (noncurrent liabilities)	0		0
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)	$ 0		$ 0

[1] Prior to the merger, the five-year financial swap contract between Generation and ComEd was de-designated. As a result, all prospective changes in fair value are recorded to operating revenues and eliminated in consolidation.

[2] Includes $15 million and $9 million of losses, net of taxes, related to the effective portion of changes in fair value of interest rate swaps and treasury rate locks at Generation for the year ended December 31, 2013 and 2012, respectively

[3] Exelon and Generation have historically presented mark-to-market gains and losses within purchased power expense for all non-trading, energy-related derivatives that were not accounted for as cash flow hedges. In 2011, Exelon and Generation classified the mark-to-market gains and losses for contracts, where the underlying hedged transaction was an expected sale to hedge power, to operating revenues.

[4] 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

[5] Current and noncurrent assets are shown net of collateral of $84 million and $72 million, respectively, and current and noncurrent liabilities are shown net of collateral of $(12) million and $0 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $144 million at December 31, 2013.

[6] 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

[7] 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

[8] Includes $133 million and $420 million of gains, net of taxes, related to the fair value of the five-year financial swap contract with ComEd for the years ended December 31, 2012 and 2011

[9] Excludes $5 million of losses and $20 million of losses, net of taxes, related to interest rate swaps and treasury rate locks for the years ended December 31, 2013 and 2012, respectively

[10] 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 for the year ended December 31, 2012. As of the merger date, cash flow hedges were discontinued, as such, this amount represents changes in fair value prior to the merger date.

[11] Includes $133 million and $375 million of losses, net of taxes, reclassified from accumulated OCI to recognize gains in net income related to settlements of the five-year financial swap contract with ComEd for the years ended December 31, 2013 and 2012, respectively

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