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				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	$ 793		$ 425		$ 656		$ 67
Total realized / unrealized gains (losses)
Included in income	(32)		(97)		1		(78)
Included in payable for Zion Station decommissioning	0				1		0
Included in regulatory assets	(38)		43		(47)		38
Change in collateral	(30)		(15)		13		(7)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	41		18		151		437
Sales	(29)		0		(70)		(9)
Settlements	(3)				(11)
Transfers into Level 3 - (Asset) / Liability	4		0		11		(34)
Transfers out of Level 3 - (Asset) / Liability	(5)		0		(4)		(39)
Ending balance	701		375		701		375
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	51		(42)		160		62
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	240		54		183		13
Total realized / unrealized gains (losses)
Included in income	0				2
Included in regulatory assets	(1)		2		8		2
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	23		14		90		55
Sales	(14)				(27)
Settlements	(3)				(11)
Ending balance	245		70		245		70
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	0				1
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	111		59		89		37
Total realized / unrealized gains (losses)
Included in payable for Zion Station decommissioning	0		1		1		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	10		4		43		36
Sales	(15)		0		(27)		(9)
Ending balance	106		64		106		64
Derivative [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	431		295		367		17
Total realized / unrealized gains (losses)
Included in income	(32)	[1]	(97)	[2]	(1)	[1],[3]	(78)	[2],[4]
Included in regulatory assets	(37)		41	[5]	(55)	[6],[7]	36	[5]
Change in collateral	(30)		(15)		13		(7)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	8				16		329	[8]
Sales	0				(8)
Transfers into Level 3 - (Asset) / Liability	4		0		11		(34)
Transfers out of Level 3 - (Asset) / Liability	(5)		0		(4)		(39)
Ending balance	339		224		339		224
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	51		(42)		159		62
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	(83)		(55)		(160)		(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			310				310
Other Investments [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	11		17		17
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	0		0		2		17
Sales					(8)
Ending balance	11		17		11		17
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair value of Constellation fair value assets acquired			14				14
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	878		1,042		949		867
Total realized / unrealized gains (losses)
Included in income	(32)		(112)		(6)		(109)
Included in other comprehensive income	0		(139)		(219)		(311)
Included in payable for Zion Station decommissioning	0		1		1		0
Included in noncurrent payables to affiliates	1		(2)		8		(2)
Change in collateral	(30)		(15)		13		(7)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	41		18		151	[9]	437
Sales	(29)		0		(70)		(9)
Settlements	(3)				(11)
Transfers into Level 3 - (Asset) / Liability	4		0		11		(34)
Transfers out of Level 3 - (Asset) / Liability	(5)		0		(4)		(39)
Ending balance	823		797		823		797
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	51		(77)		149		1
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	240		54		183		13
Total realized / unrealized gains (losses)
Included in income	0				2
Included in noncurrent payables to affiliates	1		(2)		8		(2)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	23		14		90	[9]	55
Sales	(14)				(27)
Settlements	(3)				(11)
Ending balance	245		70		245		70
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	0				1
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	111		59		89		37
Total realized / unrealized gains (losses)
Included in payable for Zion Station decommissioning	0		1		1		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	10		4		43	[9]	36
Sales	(15)		0		(27)		(9)
Ending balance	106		64		106		64
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	516		912		660		817
Total realized / unrealized gains (losses)
Included in income	(32)	[10]	(112)	[11]	(8)	[12],[13]	(109)	[14],[2]
Included in other comprehensive income	0		(139)	[5]	(219)	[12],[15]	(311)	[16],[5]
Change in collateral	(30)		(15)		13		(7)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	8				16		329	[8]
Sales	0				(8)
Transfers into Level 3 - (Asset) / Liability	4		0		11		(34)
Transfers out of Level 3 - (Asset) / Liability	(5)		0		(4)		(39)
Ending balance	461		646		461		646
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	51		(77)		148		1
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	(83)		(35)		(156)		(110)
Increase (decrease) in fair value related to the swap contract	0		(35)		11		86
Realized gains (losses) related to swap contract	0		(119)		(215)		(427)
Fair value of Constellation fair value assets acquired			310				310
Acquisition of marketable securities			14				14
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	11		17		17
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	0		0		2		17
Sales					(8)
Ending balance	11		17		11		17
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	(85)		(617)		(293)		(800)
Total realized / unrealized gains (losses)
Included in regulatory assets	37		195		171		378
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Ending balance	(122)		(422)		(122)		(422)
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			(35)				86
Realized gains (losses) related to swap contract			(119)				(427)
Increase (decrease) in fair value related to floating-to-fixed energy swap contracts			(40)
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				(11)
Realized gains (losses) related to swap contract	0				215
Increase (decrease) in fair value related to floating-to-fixed energy swap contracts	$ (37)				$ 57

[1] Includes the reclassification of $83 million and $160 million of realized losses due to the settlement of derivative contracts recorded in results of operations for the three and nine months ended September 30, 2013.

[2] Includes the reclassification of $55 million and $140 million of realized losses due to the settlement of derivative contracts recorded in results of operations for the three and nine months ended September 30, 2012, respectively.

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

[4] Includes the reclassification of $##D<gpyreclasssettlment> million of realized losses due to the settlement of derivative contracts recorded in results of operations.

[5]  Excludes $35 million of decreases in fair value and $86 million of increases in fair value and $119 million and $427 million of realized losses due to settlements for the three and nine months ended September 30, 2012 of Generation’s financial swap contract with ComEd, which eliminates upon consolidation in Exelon’s Consolidated Financial Statements.

[6] Includes increases in fair value of $##D<gcomedfvpretaxytd> million and realized losses reclassified from OCI due to settlements of $##D<gcomedreclassytd> million associated with Generation's financial swap contract with ComEd for the ##D<curmonth> months ended ##D<cyperiod>, respectively. All items eliminate upon consolidation in Exelon's Consolidated Financial Statements.

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

[8] Includes $310 million of fair value from contracts and $14 million of other investments acquired as a result of the merger.

[9] (c) Includes $##D<gfvacquiredq1> million of fair value from contracts and $##D<gfvothinvestq1> million of other investments acquired as a result of the merger.

[10] 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

[11] )         Includes the reclassification of $35 million and $110 million of realized losses due to the settlement of derivative contracts recorded in results of operations for the three and nine months ended September 30, 2012, respectively.

[12] 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

[13] (a) Includes the reclassification of $##D<gcyrclrellossq1> million of realized losses due to the settlement of derivative contracts recorded in results of operations.

[14] (a) Includes the reclassification of $##D<gpyreclasssettlmentq1> million of realized losses due to the settlement of derivative contracts recorded in results of operations.

[15] (b) Includes $##D<gcomedfvpretaxqtdq1> million of increases in fair value and $##D<gcomedreclassqtdq1> million of realized losses due to settlements during ##D<cyfiscal> of Generation's financial swap contract with ComEd, which eliminates upon consolidation in Exelon's Consolidated Financial Statements.

[16] (b) Includes $##D<gpycomedfvpretaxqtdq1> million of increases in fair value and $##D<gpycomedreclassqtdq1> million of realized losses due to settlements during ##D<pyfiscal> of Generation's financial swap contract with ComEd, which eliminates upon consolidation in Exelon's Consolidated Financial Statements.