Fair Value of Financial Assets and Liabilities (Fair Value Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	$ 752		$ 583		$ 749		$ 656
Total realized / unrealized gains (losses)
Included in income	(46)		159		(357)		33
Included in payable for Zion Station decommissioning	4				4		1
Included in regulatory assets	42		(2)		70		(9)
Change in collateral	34		10		178		43
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	127		61		308		110
Sales	(26)		(20)		(33)		(41)
Settlements	(12)		3		(19)
Transfers into Level 3 - (Asset) / Liability	(4)		3		(30)		7
Transfers out of Level 3 - (Asset) / Liability	(28)		1		(27)		1
Ending balance	843		793		843		793
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	21		188		(425)		109
Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	486		210		350		183
Total realized / unrealized gains (losses)
Included in income	2				3
Included in regulatory assets	8		8		11		9
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	109		35		249		67
Sales	(1)				(2)
Settlements	(12)				(19)
Ending balance	592		240		592		240
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	2				2
Pledged Assets For Zion Station Decommissioning [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	137		104		112		89
Total realized / unrealized gains (losses)
Included in payable for Zion Station decommissioning	4		1		4		1
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	13		11		42		33
Sales	(21)		(5)		(25)		(12)
Ending balance	133		111		133		111
Derivative [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	119		260		272		367
Total realized / unrealized gains (losses)
Included in income	(48)	[1]	158	[2]	(360)	[1]	31	[2]
Included in regulatory assets	34		(10)	[3]	59		(18)	[3]
Change in collateral	34		10		178		43
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	5				15		8	[4]
Sales	(4)				(6)
Transfers into Level 3 - (Asset) / Liability	(4)		3		(30)		7
Transfers out of Level 3 - (Asset) / Liability	(28)		1		(20)		1
Ending balance	108		431		108		431
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	19		187		(427)		108
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Gain (loss) reclassified to results of operating due to the settlement of derivative contracts	(67)		(55)		67		(140)
Increase (decrease) in fair value related to the swap contract	(3)		(35)		(11)		(86)
Realized gains (losses) related to swap contract with unaffiliated parties	(82)		(119)		(215)		(427)
Fair value of Constellation fair value assets acquired			10				10
Other Investments [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	10		9		15
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	0		2		2		2
Sales					0
Ending balance	10		11		10		11
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	920		743		942		949
Total realized / unrealized gains (losses)
Included in income	(46)		169		(357)		26
Included in other comprehensive income	0		(95)		0		(219)
Included in payable for Zion Station decommissioning	4		1		4		1
Included in noncurrent payables to affiliates	(8)		(8)		11		(9)
Change in collateral	34		10		178		43
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	127		61		308		110
Sales	(26)		(20)		(33)		(41)
Settlements	(12)				(19)
Transfers into Level 3 - (Asset) / Liability	(4)		3		(30)		7
Transfers out of Level 3 - (Asset) / Liability	(28)		1		(27)		1
Ending balance	977		878		977		878
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	21		184		(425)		98
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair value of Constellation fair value assets acquired	310				310
Acquisition of marketable securities	14				14
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	486		210		350		183
Total realized / unrealized gains (losses)
Included in income	2				3
Included in noncurrent payables to affiliates	(8)		(8)		11		(9)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	109		35		249		67
Sales	(1)				(2)
Settlements	(12)				(19)
Ending balance	592		240		592		240
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	2				2
Exelon Generation Co L L C [Member] | Pledged Assets For Zion Station Decommissioning [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	137		104		112		89
Total realized / unrealized gains (losses)
Included in payable for Zion Station decommissioning	4		1		4		1
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	13		11		42		33
Sales	(21)		(5)		(25)		(12)
Ending balance	133		111		133		111
Exelon Generation Co L L C [Member] | Derivative [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	287		420		465		660
Total realized / unrealized gains (losses)
Included in income	(48)	[5]	168	[6]	(360)	[7]	24	[2]
Included in other comprehensive income	0		(95)	[3]	0	[7]	(219)	[3]
Change in collateral	34		10		178		43
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	5				15		8	[4]
Sales	(4)				(6)
Transfers into Level 3 - (Asset) / Liability	(4)		3		(30)		7
Transfers out of Level 3 - (Asset) / Liability	(28)		1		(20)		1
Ending balance	242		516		242		516
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	19		183		(427)		97
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Gain (loss) reclassified to results of operating due to the settlement of derivative contracts	(67)		(15)		67		(73)
Increase (decrease) in fair value related to the swap contract	0		(3)		0		11
Realized gains (losses) related to swap contract	0		(82)		0		(215)
Fair value of Constellation fair value assets acquired			10				10
Payment For Purchase Contracts	10				10
Exelon Generation Co L L C [Member] | Other Investments [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	10		9		15
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	0		2		2		2
Sales					0
Ending balance	10		11		10		11
Commonwealth Edison Co [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Increase (decrease) in fair value related to the swap contract			7				5
Realized gains (losses) related to swap contract			88				309
Realized gains (losses) related to swap contract with unaffiliated parties	(1)				(2)
Increase (decrease) in fair value related to floating-to-fixed energy swap contracts			(19)				(54)
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	(168)		(160)		(193)		(293)
Total realized / unrealized gains (losses)
Included in regulatory assets	(34)		75		59		208
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Ending balance	(134)		(85)		(134)		(85)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Increase (decrease) in fair value related to the swap contract			(3)				11
Realized gains (losses) related to swap contract			(82)				(215)
Increase (decrease) in fair value related to floating-to-fixed energy swap contracts			(9)
Commonwealth Edison Co [Member] | Derivative [Member] | Fair Value Inputs Level 3 [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Increase (decrease) in fair value related to the swap contract	0				0
Realized gains (losses) related to swap contract	0				0
Increase (decrease) in fair value related to floating-to-fixed energy swap contracts	$ (34)				$ 64

[1] Includes the increase for the reclassification of $67 million of realized losses due to the settlement of derivative contracts recorded in results of operations for the three months ended June 30, 2014.

[2] Includes the reclassification of $29 million and $77 million of realized losses due to the settlement of derivative contracts recorded in results of operations for the three and six months ended June 30, 2013, respectively.

[3]  Excludes decreases in fair value of $3 million and $11 million and realized losses reclassified due to settlements of $82 million and $215 million associated with Generation’s financial swap contract with ComEd for the three and six months ended June 30, 2013. All items eliminate upon consolidation in Exelon’s Consolidated Financial Statements.

[4] Includes $10 million which Generation was paid to enter into out of the money purchase contracts.

[5] Includes the reclassification of $##D<gqtdreclasssettlement> million and $##D<gytdreclasssettlement> million of realized losses due to the settlement of derivative contracts recorded in results of operations for the three and ##D<curmonth> months ended ##D<cyperiod>, respectively

[6] )         Includes the reclassification of $15 million and $73 million of realized losses due to the settlement of derivative contracts recorded in results of operations for the three and six months ended June 30, 2013, respectively.

[7] Includes $##D<gcomedfvpretaxqtd> million of decreases in fair value and $121 million of increases in fair value and realized losses due to settlements of $##D<gcomedreclassqtd> million and $308 million associated with Generation's financial swap contract with ComEd for the ##D<threemonth> and ##D<curmonth> months ended ##D<cyperiod>, respectively. This position was de-designated as a cash flow hedge prior to the merger date. All prospective changes in fair value and reclassifications of realized amounts are being recorded to income offset by the amortization of the frozen mark in OCI. All items eliminate upon consolidation in Exelon's Consolidated Financial Statements