Derivative Financial Instruments (Fair Value Measurments) (Details) (USD $)	3 Months Ended				6 Months Ended				7 Months Ended		9 Months Ended				12 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Sep. 30, 2012		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011		Dec. 31, 2010
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Ineffective portion recognized in income															$ 0
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Net gain (loss) of reclassifications from accumulated OCI to net income related to settlements of block contracts													(2,000,000)
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	145,000,000		74,000,000								548,000,000		305,000,000
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets (current assets)	906,000,000								906,000,000		906,000,000				432,000,000
Mark-to-market derivative assets with affiliate (current assets)	0								0		0				0
Mark-to-market derivative assets (noncurrent assets)	937,000,000								937,000,000		937,000,000				650,000,000
Mark-to-market derivative assets with affiliate (noncurrent assets)															0
Total mark-to-market derivative assets	1,843,000,000								1,843,000,000		1,843,000,000				1,082,000,000
Mark-to-market derivative liabilities (current liabilities)	(499,000,000)								(499,000,000)		(499,000,000)				(112,000,000)
Mark-to-market derivative liability with affiliate (current liability)	0								0		0				0
Mark-to-market energy derivative liabilities (noncurrent liabilities)	(335,000,000)								(335,000,000)		(335,000,000)				(107,000,000)
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)															0
Total mark-to-market derivative liabilities	(834,000,000)								(834,000,000)		(834,000,000)				(219,000,000)
Total mark-to-market derivative net assets (liabilities)	1,009,000,000								1,009,000,000		1,009,000,000				863,000,000
Footnotes To Derivative Instruments In Statement Of Financial Position Fair Value [Abstract]
Fair value swap contract current liability															503,000,000
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	(91,000,000)		22,000,000								98,000,000		13,000,000
Reclassification to realized at settlement	123,000,000		(101,000,000)								216,000,000		(372,000,000)
Net mark-to-market gains (losses)	32,000,000		(79,000,000)								314,000,000		(359,000,000)
Operating Revenue [Member]
Proprietary Trading Activities [Abstract]
Change in fair value	(2,000,000)		2,000,000								12,000,000		22,000,000
Reclassification to realized at settlement	25,000,000		(6,000,000)								57,000,000		(19,000,000)
Net mark-to-market gains (losses)	23,000,000		(4,000,000)								69,000,000		3,000,000
Pro Forma [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value			22,000,000										13,000,000
Reclassification to realized at settlement			(101,000,000)										(372,000,000)
Net mark-to-market gains (losses)			(79,000,000)										(359,000,000)
Operating Revenue [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value			0										0
Reclassification to realized at settlement			0										0
Net mark-to-market gains (losses)			0										0
Operating Revenue [Member] | Pro Forma [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value			31,000,000										44,000,000
Reclassification to realized at settlement			(105,000,000)										(374,000,000)
Net mark-to-market gains (losses)			(74,000,000)										(330,000,000)
Purchased Power And Fuel [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value			22,000,000										13,000,000
Reclassification to realized at settlement			(101,000,000)										(372,000,000)
Net mark-to-market gains (losses)			(79,000,000)										(359,000,000)
Purchased Power And Fuel [Member] | Pro Forma [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value			(9,000,000)										(31,000,000)
Reclassification to realized at settlement			4,000,000										2,000,000
Net mark-to-market gains (losses)			(5,000,000)										(29,000,000)
Total Cash Flow Hedges [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Accumulated OCI derivative gain - Beginning Balance	547,000,000		209,000,000		488,000,000		400,000,000				488,000,000		400,000,000		400,000,000
Effective portion of changes in fair value	0		(26,000,000)								300,500,000	[1]	(73,000,000)
Accumulated OCI derivative gain - Ending Balance	459,000,000		145,000,000						459,000,000		459,000,000		145,000,000
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											(23,000,000)
Total Cash Flow Hedges [Member] | Operating Revenue [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Reclassifications from accumulated OCI to net income	(88,000,000)		(45,000,000)								(332,000,000)		(184,000,000)
Ineffective portion recognized in income											2,500,000		2,000,000
Total Cash Flow Hedges [Member] | Purchased Power [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Ineffective portion recognized in income	0		7,000,000
Exelon Generation Co L L C [Member]
Cash Flow Hedge Activity Impact [Abstract]
Net unrealized pre-tax gain (loss) on effective cash flow hedges											1,928,000,000
Net unrealized pre-tax gain (loss) on effective cash flow hedges related to swap contract											693,000,000
Expected reclassification from accumulated other comprehensive income to results of operations related to fair value of swap contracts											383,000,000
Cash flow hedge activity impact on pre-tax net income based on reclassification adjustment from accumulated other comprehensive income	283,000,000		162,000,000								1,005,000,000		617,000,000
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets (current assets)	906,000,000	[2]							906,000,000	[2]	906,000,000	[2]			432,000,000	[3]
Mark-to-market derivative assets with affiliate (current assets)	352,000,000	[2]							352,000,000	[2]	352,000,000	[2]			503,000,000	[3]
Mark-to-market derivative assets (noncurrent assets)	937,000,000	[2]							937,000,000	[2]	937,000,000	[2]			635,000,000	[3]
Mark-to-market derivative assets with affiliate (noncurrent assets)	0								0		0				191,000,000	[3]
Total mark-to-market derivative assets	2,195,000,000	[2]							2,195,000,000	[2]	2,195,000,000	[2]			1,761,000,000	[3]
Mark-to-market derivative liabilities (current liabilities)	(482,000,000)	[2]							(482,000,000)	[2]	(482,000,000)	[2]			(103,000,000)	[3]
Mark-to-market derivative liability with affiliate (current liability)	0								0		0				0
Mark-to-market energy derivative liabilities (noncurrent liabilities)	(282,000,000)	[2]							(282,000,000)	[2]	(282,000,000)	[2]			(10,000,000)	[3]
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)															0
Total mark-to-market derivative liabilities	(764,000,000)	[2]							(764,000,000)	[2]	(764,000,000)	[2]			(113,000,000)	[3]
Total mark-to-market derivative net assets (liabilities)	1,431,000,000	[2]							1,431,000,000	[2]	1,431,000,000	[2]			1,648,000,000	[3]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	(126,000,000)		22,000,000								36,000,000		13,000,000
Reclassification to realized at settlement	142,000,000		(101,000,000)								245,000,000		(372,000,000)
Net mark-to-market gains (losses)	16,000,000		(79,000,000)								281,000,000		(359,000,000)	[4]
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Proprietary Trading Activities [Abstract]
Change in fair value	(2,000,000)		2,000,000								12,000,000		22,000,000
Reclassification to realized at settlement	25,000,000		(6,000,000)								57,000,000		(19,000,000)
Net mark-to-market gains (losses)	23,000,000		(4,000,000)								69,000,000		3,000,000
Exelon Generation Co L L C [Member] | Pro Forma [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value			22,000,000										13,000,000
Reclassification to realized at settlement			(101,000,000)										(372,000,000)
Net mark-to-market gains (losses)			(79,000,000)										(359,000,000)
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	(255,000,000)		0								(85,000,000)		0
Reclassification to realized at settlement	20,000,000		0								(81,000,000)		0
Net mark-to-market gains (losses)	(235,000,000)		0								(166,000,000)		0	[4]
Exelon Generation Co L L C [Member] | Operating Revenue [Member] | Business Intersegment Eliminations [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	35,000,000										62,000,000
Reclassification to realized at settlement	(19,000,000)										(29,000,000)
Net mark-to-market gains (losses)	16,000,000										33,000,000
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			31,000,000										44,000,000
Reclassification to realized at settlement			(105,000,000)										(374,000,000)
Net mark-to-market gains (losses)			(74,000,000)										(330,000,000)
Exelon Generation Co L L C [Member] | Purchased Power And Fuel [Member]
Other Derivatives Not Designated As Hedging Instruments [Abstract]
Change in fair value	129,000,000		22,000,000								121,000,000		13,000,000
Reclassification to realized at settlement	122,000,000		(101,000,000)								326,000,000		(372,000,000)
Net mark-to-market gains (losses)	251,000,000		(79,000,000)								447,000,000		(359,000,000)	[4]
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			(9,000,000)										(31,000,000)
Reclassification to realized at settlement			4,000,000										2,000,000
Net mark-to-market gains (losses)			(5,000,000)										(29,000,000)
Exelon Generation Co L L C [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets (current assets)	3,399,000,000	[5]							3,399,000,000	[5]	3,399,000,000	[5]			1,195,000,000
Mark-to-market derivative assets with affiliate (current assets)	352,000,000	[5]							352,000,000	[5]	352,000,000	[5]			0
Mark-to-market derivative assets (noncurrent assets)	2,133,000,000	[5]							2,133,000,000	[5]	2,133,000,000	[5]			582,000,000
Mark-to-market derivative assets with affiliate (noncurrent assets)															0
Total mark-to-market derivative assets	5,884,000,000	[5]							5,884,000,000	[5]	5,884,000,000	[5]			1,777,000,000
Mark-to-market derivative liabilities (current liabilities)	(2,951,000,000)	[5]							(2,951,000,000)	[5]	(2,951,000,000)	[5]			(965,000,000)
Mark-to-market derivative liability with affiliate (current liability)	0	[5]							0	[5]	0	[5]			0
Mark-to-market energy derivative liabilities (noncurrent liabilities)	(1,369,000,000)	[5]							(1,369,000,000)	[5]	(1,369,000,000)	[5]			(186,000,000)
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)															0
Total mark-to-market derivative liabilities	(4,320,000,000)	[5]							(4,320,000,000)	[5]	(4,320,000,000)	[5]			(1,151,000,000)
Total mark-to-market derivative net assets (liabilities)	1,564,000,000	[5]							1,564,000,000	[5]	1,564,000,000	[5]			626,000,000
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Footnotes To Derivative Instruments In Statement Of Financial Position Fair Value [Abstract]
Current assets collateral offset	92,000,000								92,000,000		92,000,000				338,000,000
Noncurrent assets collateral offset	263,000,000								263,000,000		263,000,000				187,000,000
Current liabilities collateral offset	(49,000,000)								(49,000,000)		(49,000,000)				15,000,000
Noncurrent liabilities collateral offset	(113,000,000)								(113,000,000)		(113,000,000)				0
Total cash collateral received net of cash collateral posted															540,000,000
Exelon Generation Co L L C [Member] | Cash Flow Hedging [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets (current assets)															438,000,000	[6]
Mark-to-market derivative assets with affiliate (current assets)															503,000,000	[6]
Mark-to-market derivative assets (noncurrent assets)															419,000,000	[6]
Mark-to-market derivative assets with affiliate (noncurrent assets)															191,000,000	[6]
Total mark-to-market derivative assets															1,551,000,000	[6]
Mark-to-market derivative liabilities (current liabilities)															(9,000,000)	[6]
Mark-to-market derivative liability with affiliate (current liability)															0
Mark-to-market energy derivative liabilities (noncurrent liabilities)															(4,000,000)	[6]
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)															0
Total mark-to-market derivative liabilities															(13,000,000)	[6]
Total mark-to-market derivative net assets (liabilities)															1,538,000,000	[6]
Footnotes To Derivative Instruments In Statement Of Financial Position Fair Value [Abstract]
Fair value swap contract current asset	352,000,000								352,000,000		352,000,000				503,000,000
Fair value swap contract noncurrent asset															191,000,000
Noncurrent liability DOE interest rate swap															19,000,000
Exelon Generation Co L L C [Member] | Proprietary Trading [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets (current assets)	3,694,000,000								3,694,000,000		3,694,000,000				217,000,000
Mark-to-market derivative assets with affiliate (current assets)	0								0		0				0
Mark-to-market derivative assets (noncurrent assets)	1,147,000,000								1,147,000,000		1,147,000,000				71,000,000
Mark-to-market derivative assets with affiliate (noncurrent assets)															0
Total mark-to-market derivative assets	4,841,000,000								4,841,000,000		4,841,000,000				288,000,000
Mark-to-market derivative liabilities (current liabilities)	(3,675,000,000)								(3,675,000,000)		(3,675,000,000)				(194,000,000)
Mark-to-market derivative liability with affiliate (current liability)	0								0		0				0
Mark-to-market energy derivative liabilities (noncurrent liabilities)	(1,106,000,000)								(1,106,000,000)		(1,106,000,000)				(70,000,000)
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)															0
Total mark-to-market derivative liabilities	(4,781,000,000)								(4,781,000,000)		(4,781,000,000)				(264,000,000)
Total mark-to-market derivative net assets (liabilities)	60,000,000								60,000,000		60,000,000				24,000,000
Exelon Generation Co L L C [Member] | Collateral And Netting [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets (current assets)	(6,187,000,000)	[7]							(6,187,000,000)	[7]	(6,187,000,000)	[7]			(1,418,000,000)	[7]
Mark-to-market derivative assets with affiliate (current assets)	0								0		0				0
Mark-to-market derivative assets (noncurrent assets)	(2,343,000,000)	[7]							(2,343,000,000)	[7]	(2,343,000,000)	[7]			(437,000,000)	[7]
Mark-to-market derivative assets with affiliate (noncurrent assets)															0
Total mark-to-market derivative assets	(8,530,000,000)	[7]							(8,530,000,000)	[7]	(8,530,000,000)	[7]			(1,855,000,000)	[7]
Mark-to-market derivative liabilities (current liabilities)	6,144,000,000	[7]							6,144,000,000	[7]	6,144,000,000	[7]			1,065,000,000	[7]
Mark-to-market derivative liability with affiliate (current liability)	0								0		0				0
Mark-to-market energy derivative liabilities (noncurrent liabilities)	2,193,000,000	[7]							2,193,000,000	[7]	2,193,000,000	[7]			250,000,000	[7]
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)															0
Total mark-to-market derivative liabilities	8,337,000,000	[7]							8,337,000,000	[7]	8,337,000,000	[7]			1,315,000,000	[7]
Total mark-to-market derivative net assets (liabilities)	(193,000,000)	[7]							(193,000,000)	[7]	(193,000,000)	[7]			(540,000,000)	[7]
Footnotes To Derivative Instruments In Statement Of Financial Position Fair Value [Abstract]
Total cash collateral received net of cash collateral posted	193,000,000								193,000,000		193,000,000
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	923,000,000	[8],[9]	688,000,000	[10]	925,000,000	[11],[12]	1,011,000,000	[13]			925,000,000	[11],[12]	1,011,000,000	[13]	1,011,000,000	[13]
Effective portion of changes in fair value	0	[14]	(26,000,000)	[15]							432,000,000	[16]	(69,000,000)	[17]
Accumulated OCI derivative gain - Ending Balance	752,000,000	[11],[12]	571,000,000	[13],[18]	923,000,000	[8],[9]	688,000,000	[10]	752,000,000	[11],[12]	752,000,000	[11],[12]	571,000,000	[13],[18]	925,000,000	[11],[12]	1,011,000,000	[13]
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Unrealized gain (loss) related to fair value of swap contract	232,000,000		400,000,000		315,000,000		458,000,000		232,000,000		232,000,000		400,000,000				589,000,000
Unrealized gain (loss) related to fair value of block contract			1,000,000				2,000,000						1,000,000				3,000,000
Net gain (loss) related to effective portion of changes in fair value of swap contract									88,000,000		232,000,000				420,000,000
Net gains related to effective portion of changes in fair value of financial block contract			(5,000,000)
Net gains (losses) related to interest rate swaps and treasury rate locks	(22,000,000)		(6,000,000)		22,000,000		2,000,000				(22,000,000)						(10,000,000)
Net gain (loss) related to effective portion of changes in fair value of treasury rate locks													(2,000,000)
Exelon Generation Co L L C [Member] | Energy Related Hedges [Member] | Operating Revenue [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Reclassifications from accumulated OCI to net income	(171,000,000)	[19]	(98,000,000)	[20]							(608,000,000)	[21]	(373,000,000)	[22]
Ineffective portion recognized in income			7,000,000								3,000,000		2,000,000
Footnotes To Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Net gain (loss) of reclassifications from accumulated OCI to net income related to the settlements of swap contract	(83,000,000)		(53,000,000)								(276,000,000)		(187,000,000)
Net gain (loss) of reclassifications from accumulated OCI to net income related to settlements of block contracts			(1,000,000)
Exelon Generation Co L L C [Member] | Energy Related Hedges [Member] | Purchased Power [Member]
Cash Flow Hedge Accumulated Other Comprehensive Income [Abstract]
Ineffective portion recognized in income	0
Commonwealth Edison Co [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative liability with affiliate (current liability)	(352,000,000)								(352,000,000)		(352,000,000)				(503,000,000)
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)	0								0		0				(191,000,000)
Commonwealth Edison Co [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets (current assets)	0	[5]							0	[5]	0	[5]			0
Mark-to-market derivative assets with affiliate (current assets)	0	[5]							0	[5]	0	[5]			0
Mark-to-market derivative assets (noncurrent assets)	0	[5]							0	[5]	0	[5]			0
Mark-to-market derivative assets with affiliate (noncurrent assets)															0
Total mark-to-market derivative assets	0	[5]							0	[5]	0	[5]			0
Mark-to-market derivative liabilities (current liabilities)	(17,000,000)	[23]							(17,000,000)	[23]	(17,000,000)	[23]			(9,000,000)	[23]
Mark-to-market derivative liability with affiliate (current liability)	(352,000,000)	[5]							(352,000,000)	[5]	(352,000,000)	[5]			(503,000,000)	[6]
Mark-to-market energy derivative liabilities (noncurrent liabilities)	(53,000,000)	[23]							(53,000,000)	[23]	(53,000,000)	[23]			(97,000,000)	[23]
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)															(191,000,000)	[6]
Total mark-to-market derivative liabilities	(422,000,000)	[23],[5]							(422,000,000)	[23],[5]	(422,000,000)	[23],[5]			(800,000,000)	[23],[6]
Total mark-to-market derivative net assets (liabilities)	(422,000,000)	[23],[5]							(422,000,000)	[23],[5]	(422,000,000)	[23],[5]			(800,000,000)	[23],[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	352,000,000								352,000,000		352,000,000
Fair value swap contract noncurrent liability															191,000,000
PECO Energy Co [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative liabilities (current liabilities)	0								0		0				0
Mark-to-market derivative liability with affiliate (current liability)	0								0		0				0
Other Segment [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets (current assets)	0	[5]							0	[5]	0	[5]
Other Segment [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets (current assets)															0
Mark-to-market derivative assets with affiliate (current assets)															0
Mark-to-market derivative assets (noncurrent assets)															15,000,000
Mark-to-market derivative assets with affiliate (noncurrent assets)															0
Total mark-to-market derivative assets															15,000,000
Mark-to-market derivative liabilities (current liabilities)															0
Mark-to-market derivative liability with affiliate (current liability)															0
Mark-to-market energy derivative liabilities (noncurrent liabilities)															0
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)															0
Total mark-to-market derivative liabilities															0
Total mark-to-market derivative net assets (liabilities)															15,000,000
Other Segment [Member] | Business Intersegment Eliminations [Member]
Derivatives Fair Value [Line Items]
Mark-to-market derivative assets (current assets)															0
Mark-to-market derivative assets with affiliate (current assets)	(352,000,000)	[5]							(352,000,000)	[5]	(352,000,000)	[5]			(503,000,000)	[6]
Mark-to-market derivative assets (noncurrent assets)	0	[5]							0	[5]	0	[5]			0
Mark-to-market derivative assets with affiliate (noncurrent assets)															(191,000,000)	[6]
Total mark-to-market derivative assets	(352,000,000)	[5]							(352,000,000)	[5]	(352,000,000)	[5]			(694,000,000)	[6]
Mark-to-market derivative liabilities (current liabilities)	0	[5]							0	[5]	0	[5]			0
Mark-to-market derivative liability with affiliate (current liability)	352,000,000	[5]							352,000,000	[5]	352,000,000	[5]			503,000,000	[6]
Mark-to-market energy derivative liabilities (noncurrent liabilities)	0	[5]							0	[5]	0	[5]			0
Mark-to-market derivative liabilities with affiliate (noncurrent liabilities)															191,000,000	[6]
Total mark-to-market derivative liabilities	352,000,000	[5]							352,000,000	[5]	352,000,000	[5]			694,000,000	[6]
Total mark-to-market derivative net assets (liabilities)	$ 0	[5]							$ 0	[5]	$ 0	[5]			$ 0

[1] Includes $12 million of losses, net of taxes, related to the effective portion of changes in fair value of interest rate swaps and treasury rate locks.

[2] Current and noncurrent assets are shown net of collateral of $92 million and $263 million, respectively, and current and noncurrent liabilities are shown net of collateral of $(49) million and $(113) million, respectively. The total cash collateral received, net of cash collateral posted and offset against mark-to-market assets and liabilities was $193 million at September 30, 2012.

[3] Current and noncurrent assets are shown net of collateral of $338 million and $187 million, respectively, and current and noncurrent liabilities are shown inclusive of collateral of $15 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 $540 million at December 31, 2011.

[4] 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

[5] Includes current assets for Generation and current liabilities for ComEd of $352 million related to the fair value of the five-year financial swap contract between Generation and ComEd, as described above.

[6] Includes current and noncurrent assets for Generation and current and noncurrent liabilities for ComEd of $503 million and $191 million, respectively, related to the fair value of the five-year financial swap contract between Generation and ComEd, as described above. For Generation excludes $19 million noncurrent liability relating to an interest rate swap in connection with a loan agreement to fund Antelope Valley as discussed above.

[7] Represents the netting of fair value balances with the same counterparty and the application of collateral.

[8] Includes $232 million and $315 million of gains, net of taxes, related to the fair value of the five-year financial swap contract with ComEd, as of September 30, 2012 and June 30, 2012, respectively.

[9] Excludes $22 million of losses and $22 million of losses net of taxes, related to interest rate swaps and treasury rate locks for the three months ended September 30, 2012 and three months ended June 30, 2012.

[10] Includes $400 million and $458 million of gains, net of taxes, related to the fair value of the five-year financial swap contract with ComEd, $1 million of gains, net of taxes, related to the fair value of the block contracts with PECO as of September 30, 2011 and June 30, 2011, respectively.

[11] Includes $232 million and $420 million of gains, net of taxes, related to the fair value of the five-year financial swap contract with ComEd, as of September 30, 2012 and December 31, 2011.

[12] Excludes $22 million of losses and $10 million of losses, net of taxes, related to interest rate swaps and treasury locks for the nine months ended September 30, 2012 and year ended December 31, 2011, respectively.

[13] Includes $400 million and $589 million of gains, net of taxes, related to the fair value of the five-year financial swap contract with ComEd, and $1 million and $3 million of gains, net of taxes, related to the fair value of the block contracts with PECO as of September 30, 2011 and December 31, 2010, respectively.

[14] Includes $0 million of losses, net of taxes, related to the effective portion of changes in fair value of interest rate swaps and treasury rate locks.

[15] Includes a $5 million loss, net of taxes, related to the effective portion of changes in fair value of the five-year financial swap contract with ComEd for the three months ended September 30, 2011. The PECO block contracts were designated as normal sales as of May 31, 2010. As such, there were no effective changes in fair value of the block contracts with PECO for the three months ended September 30, 2011 as the mark-to-market balances previously recorded will be amortized over the term of the contract.

[16] 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 through the date of de-designation prior to the merger.

[17] Includes a $2 million loss, net of taxes, related to the effective portion of changes in fair value of the five-year financial swap contract with ComEd for the nine months ended September 30, 2011. The PECO block contracts were designated as normal sales as of May 31, 2010. As such, there were no additional effective changes in fair value of PECO's block contracts as the mark-to-market balances previously recorded are being amortized over the term of the contract.

[18] Excludes $6 million loss and $2 million of gains, net of taxes, related to interest rate swaps and treasury rate locks as of September 30, 2011 and December 31, 2010.

[19] Includes $83 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.

[20] Includes a $53 million loss, 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 for the three months ended September 30, 2011.

[21] Includes $276 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

[22] Includes a $187 million loss, 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 and a $2 million loss, net of taxes, reclassified from accumulated OCI to recognize gains in net income related to the fair value of the block contracts with PECO for the nine months ended September 30, 2011

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