Derivative Financial Instruments (Fair Value Measurments) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013		Dec. 31, 2012
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Ineffective portion recognized in income	$ 5
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	756				727
Mark-to-market derivative assets (noncurrent assets)	571				607
Mark-to-market derivative liabilities (current liabilities)	(251)				(159)
Mark-to-market derivative liabilities (noncurrent liabilities)	(287)				(300)
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	(682)		(329)
Reclassification to realized at settlement	(48)		(57)
Net mark-to-market gains (losses)	(730)		(386)
Operating Revenue [Member]
Proprietary Trading Activities [Abstract]
Change in fair value	(3)		(4)
Reclassification to realized at settlement	1		6
Net mark-to-market gains (losses)	(2)		2
Operating Revenue [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	0		7	[1]
Reclassification to realized at settlement	0		10	[1]
Net mark-to-market gains (losses)	0		17	[1]
Derivative [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	754				728
Mark-to-market derivative assets (noncurrent assets)	534				569
Total mark-to-market derivative assets	1,288				1,297
Mark-to-market derivative liabilities (current liabilities)	(249)				(158)
Mark-to-market derivative liabilities (noncurrent liabilities)	(271)				(285)
Total mark-to-market derivative liabilities	(520)				(443)
Total mark-to-market derivative net assets (liabilities)	768				854
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	39		99
Total Cash Flow Hedges [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Accumulated OCI derivative gain - Beginning Balance	120		368		368
Effective portion of changes in fair value	(1)	[2]	(1)	[3],[4]
Accumulated OCI derivative gain - Ending Balance	95		309
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Net gain (loss) related to effective portion of changes in fair value of treasury rate locks			(3)
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	(24)		(58)
Exelon Generation Co L L C [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Reclassifications from accumulated OCI to net income	4,056		3,141
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	156
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	39		223
Change in cash flow hedge ineffectiveness	0		5
Cash flow hedge ineffectiveness adjustment to accumulated other comprehensive income			5
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	756				727
Mark-to-market derivative assets with affiliate (current assets)	0				0
Mark-to-market derivative assets (noncurrent assets)	561				600
Mark-to-market derivative assets with affiliate (noncurrent assets)	0				0
Mark-to-market derivative liabilities (current liabilities)	(238)				(142)
Mark-to-market derivative liabilities (noncurrent liabilities)	(131)				(120)
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	(682)		(336)
Reclassification to realized at settlement	(48)		(67)
Net mark-to-market gains (losses)	(730)		(403)
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Proprietary Trading Activities [Abstract]
Change in fair value	(3)		(4)
Reclassification to realized at settlement	1		6
Net mark-to-market gains (losses)	(2)		2
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	(853)		(485)
Reclassification to realized at settlement	93		(101)
Net mark-to-market gains (losses)	(760)		(586)
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	171		149
Reclassification to realized at settlement	(141)		34
Net mark-to-market gains (losses)	30		183
Exelon Generation Co L L C [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	754	[5]			728	[6]
Mark-to-market derivative assets (noncurrent assets)	534	[5]			569	[6]
Total mark-to-market derivative assets	1,288	[5]			1,297	[6]
Mark-to-market derivative liabilities (current liabilities)	(236)	[5]			(141)	[6]
Mark-to-market derivative liabilities (noncurrent liabilities)	(116)	[5]			(109)	[6]
Total mark-to-market derivative liabilities	(352)	[5]			(250)	[6]
Total mark-to-market derivative net assets (liabilities)	936	[5]			1,047	[6]
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	3,401				2,616
Mark-to-market derivative assets (noncurrent assets)	1,240				1,344
Total mark-to-market derivative assets	4,641				3,960
Mark-to-market derivative liabilities (current liabilities)	(3,348)				(2,023)
Mark-to-market derivative liabilities (noncurrent liabilities)	(947)				(804)
Total mark-to-market derivative liabilities	(4,295)				(2,827)
Total mark-to-market derivative net assets (liabilities)	346				1,133
Footnotes To Derivative Instruments In Statement Of Financial Position Fair Value [Abstract]
Current assets collateral offset	(179)				84
Noncurrent assets collateral offset	(36)				72
Current liabilities collateral offset	(252)				(12)
Noncurrent liabilities collateral offset	(100)				0
Total cash collateral received net of cash collateral posted	(567)				144
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
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	1,146				1,476
Mark-to-market derivative assets (noncurrent assets)	195				285
Total mark-to-market derivative assets	1,341				1,761
Mark-to-market derivative liabilities (current liabilities)	(1,112)				(1,410)
Mark-to-market derivative liabilities (noncurrent liabilities)	(206)				(293)
Total mark-to-market derivative liabilities	(1,318)				(1,703)
Total mark-to-market derivative net assets (liabilities)	23				58
Exelon Generation Co L L C [Member] | Collateral And Netting [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets	(3,793)	[7]			(3,364)	[7]
Mark-to-market derivative assets (noncurrent assets)	(901)	[7]			(1,060)	[7]
Total mark-to-market derivative assets	(4,694)	[7]			(4,424)	[7]
Mark-to-market derivative liabilities (current liabilities)	4,224	[7]			3,292	[7]
Mark-to-market derivative liabilities (noncurrent liabilities)	1,037	[7]			988	[7]
Total mark-to-market derivative liabilities	5,261	[7]			4,280	[7]
Total mark-to-market derivative net assets (liabilities)	567	[7]			(144)	[7]
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	119	[8],[9]	532	[10],[11],[12],[13]	532	[10],[11],[12],[13]
Effective portion of changes in fair value			0	[14]
Accumulated OCI derivative gain - Ending Balance	95	[8],[9]	397	[10],[11],[12],[13]	119	[8],[9]	532	[10],[11],[12],[13]
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Unrealized gain (loss) related to fair value of swap contract			58				133
Net gain (loss) of reclassifications from accumulated OCI to net income related to the settlements of swap contract			(75)
Net gains (losses) related to interest rate swaps and treasury rate locks	(3)		(16)		(15)		20
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	(24)		(135)	[15]
Commonwealth Edison Co [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative liabilities (current liabilities)	(13)				(17)
Mark-to-market derivative liability with affiliate (current liability)	0				0
Mark-to-market derivative liabilities (noncurrent liabilities)	(155)				(176)
Commonwealth Edison Co [Member] | Designated as Hedging Instrument [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative liabilities (current liabilities)	(13)	[16]			(17)
Mark-to-market derivative liabilities (noncurrent liabilities)	(155)	[16]			(176)
Total mark-to-market derivative liabilities	(168)	[16]			(193)
Total mark-to-market derivative net assets (liabilities)	(168)	[16]			(193)
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
Fair value swap contract noncurrent liability					$ 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 were recorded to operating revenues and eliminated in consolidation.

[2] Includes $##D<gytdgleffectiveintswaplock> million of losses, net of taxes, related to the effective portion of changes in fair value of interest rate swaps and treasury rate locks.

[3] Includes $3 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 $##D<gpyinterestrateswaps> 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 $(179) million and $(36) million, respectively, and current and noncurrent liabilities are shown net of collateral of $(252) million and $(100) million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $567 million at March 31, 2014.

[6] (b)        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 received, net of cash collateral posted and offset against mark-to-market assets and liabilities was $144 million at December 31, 2013.

[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] Excludes $3 million and $15 million of gains, net of taxes, related to interest rate swaps and treasury rate locks as of March 31, 2014 and December 31, 2013.

[9] Excludes $##D<ginterestrateswaps> million of losses and $##D<gpyglintswaptratelock> million of losses, net of taxes, related to interest rate swaps and treasury locks as of ##D<cyperiod> and ##D<pyend>, respectively.

[10] Includes $58 million and $133 million of gains, net of taxes, related to the fair value of the five-year financial swap contract with ComEd, as of March 31, 2013 and December 31, 2012, respectively.

[11] Excludes $16 million of losses and $20 million of losses, net of taxes, related to interest rate swaps and treasury rate locks as of March 31, 2013 and December 31, 2012, respectively.

[12] Includes $##D<gpyfyswapnot> million and $##D<gpypyefyswapnot> million of gains, net of taxes, related to the fair value of the five-year financial swap contract with ComEd, as of ##D<pyperiod> and ##D<pyend2years>.

[13] Excludes $##D<gpyinterestrateswaps> million of losses and $##D<gpypyeinterestrateswaps> million of losses, net of taxes, related to interest rate swaps and treasury rate locks for the six months ended ##D<pyperiod> and year ended ##D<pyend2years>, respectively.

[14] Includes $##D<gpyveffswapnot> 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.

[15] Includes a $75 million of losses, net of taxes, reclassified from accumulated OCI to recognize gains in net income related to the settlements of the five-year financial swap contract with ComEd

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