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, 2013	Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012
Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	$ 583	$ 428	$ 656		$ 67
Total realized / unrealized gains (losses)
Included in income	159	(64)	33		19
Included in payable for Zion Station decommissioning	1		1		(1)
Included in regulatory assets	(2)	30	(9)		(5)
Change in collateral	10	44	43		8
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	61	70	110		419
Sales	(20)	(8)	(41)		(9)
Settlements	(3)		(8)
Transfers into Level 3 - (Asset) / Liability	3	(34)	7		(34)
Transfers out of Level 3 - (Asset) / Liability	1	(40)	1		(39)
Ending balance	793	425	793		425
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	188	2	109		104
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	210	13	183		13
Total realized / unrealized gains (losses)
Included in income	1		2
Included in regulatory assets	8		9
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	35	41	67		41
Sales	(11)		(13)
Settlements	(3)		(8)
Ending balance	240	54	240		54
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	1		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	104	42	89		37
Total realized / unrealized gains (losses)
Included in payable for Zion Station decommissioning	1	(1)	1		(1)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	11	26	33		32
Sales	(5)	(8)	(12)		(9)
Ending balance	111	59	111		59
Derivative [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	260	359	367		17
Total realized / unrealized gains (losses)
Included in income	158	(64)	31	[1]	19	[2]
Included in regulatory assets	(10)	30	(18)	[3]	(5)
Change in collateral	10	44	43		8
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	13		8		329
Sales	(4)		(8)
Transfers into Level 3 - (Asset) / Liability	3	(34)	7		(34)
Transfers out of Level 3 - (Asset) / Liability	1	(40)	1		(39)
Ending balance	431	295	431		295
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	187	2	108		104
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	(29)	(66)	(77)		(85)
Increase (decrease) in fair value related to the swap contract	(3)	(14)	(11)		(121)
Realized gains (losses) related to swap contract with unaffiliated parties	(82)	(161)	(215)		(308)
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	9	14	17
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	2	3	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	743	1,251	949		867
Total realized / unrealized gains (losses)
Included in income	169	(69)	26		3
Included in other comprehensive income	(95)	(171)	(219)		(172)
Included in payable for Zion Station decommissioning	1	(1)	1		(1)
Included in noncurrent payables to affiliates	(8)		9
Change in collateral	10	44	43		8
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	61	70	110	[4]	419
Sales	(20)	(8)	(41)		(9)
Settlements	(3)		(8)
Transfers into Level 3 - (Asset) / Liability	3	(34)	7		(34)
Transfers out of Level 3 - (Asset) / Liability	1	(40)	1		(39)
Ending balance	878	1,042	878		1,042
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	184	(13)	98		78
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Fair value of Constellation fair value assets acquired	323		323
Acquisition of marketable securities	17		17
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	210	13	183		13
Total realized / unrealized gains (losses)
Included in income	1		2
Included in noncurrent payables to affiliates	(8)		9
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	35	41	67	[4]	41
Sales	(11)		(13)
Settlements	(3)		(8)
Ending balance	240	54	240		54
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	1		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	104	42	89		37
Total realized / unrealized gains (losses)
Included in payable for Zion Station decommissioning	1	(1)	1		(1)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	11	26	33	[4]	32
Sales	(5)	(8)	(12)		(9)
Ending balance	111	59	111		59
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	420	1,182	660		817
Total realized / unrealized gains (losses)
Included in income	168	(69)	24	[5]	3	[6]
Included in other comprehensive income	(95)	(171)	(219)	[7]	(172)	[8]
Change in collateral	10	44	43		8
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	13		8		329
Sales	(4)		(8)
Transfers into Level 3 - (Asset) / Liability	3	(34)	7		(34)
Transfers out of Level 3 - (Asset) / Liability	1	(40)	1		(39)
Ending balance	516	912	516		912
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	183	(13)	97		78
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	(15)	(56)	(73)		(75)
Increase (decrease) in fair value related to the swap contract	(3)	(14)	11		121
Realized gains (losses) related to swap contract	(82)	(161)	(215)		(308)
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	9	14	17
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Purchases	2	3	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			4
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	(160)	(823)	(293)		(800)
Total realized / unrealized gains (losses)
Included in regulatory assets	(75)	206	208		183
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Purchases Sales Issuances Settlements [Abstract]
Ending balance	(85)	(617)	(85)		(617)
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		(14)			121
Realized gains (losses) related to swap contract		(161)			(308)
Increase (decrease) in fair value related to floating-to-fixed energy swap contracts		(30)
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	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)		$ 20

[1] ) 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.

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

[3] 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.

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

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

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

[7] (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.

[8] (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.