Fair Value of Financial Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2011

Fair value of financial liabilities recorded at the carrying amount

	2011				2010
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt (including amounts due within one year)	$	12,627	$	14,488	$	12,213	$	12,960
Long-term debt to financing trusts		390		358		390		350
Spent nuclear fuel obligation		1,019		886		1,018		876
Preferred securities of subsidiary		87		79		87		68

Assets and liabilities measured and recorded at fair value on recurring basis

As of December 31, 2011	Level 1		Level 2		Level 3		Total
Assets
Cash equivalents(a)	$	861	$	-	$	-	$	861
Nuclear decommissioning trust fund investments
Cash equivalents		504		-		-		504
Equity
Equity securities		1,275		-		-		1,275
Commingled funds		-		1,822		-		1,822
Equity funds subtotal		1,275		1,822		-		3,097
Fixed income
Debt securities issued by the U.S. Treasury and other
U.S. government corporations and agencies		774		345		-		1,119
Debt securities issued by states of the United States
and political subdivisions of the states		-		541		-		541
Corporate debt securities		-		779		-		779
Federal agency mortgage-backed securities		-		357		-		357
Commercial mortgage-backed securities (non-agency)		-		83		-		83
Residential mortgage-backed securities (non-agency)		-		5		-		5
Mutual funds		-		47		-		47
Fixed income subtotal		774		2,157		-		2,931
Other debt obligations		-		19		13		32
Nuclear decommissioning trust fund investments subtotal(b)		2,553		3,998		13		6,564

Pledged assets for Zion decommissioning
Cash equivalents		-		-		-		-
Equity								-
Equity securities		35		-		-		35
Commingled funds		-		30		-		30
Equity funds subtotal		35		30		-		65
Fixed income
Debt securities issued by the U.S. Treasury and other
U.S. government corporations and agencies		54		26		-		80
Debt securities issued by states of the United States
and political subdivisions of the states		-		65		-		65
Corporate debt securities		-		311		-		311
Federal agency mortgage-backed securities		-		121		-		121
Commercial mortgage-backed securities (non-agency)		-		10		-		10
Commingled funds		-		20		-		20
Fixed income subtotal		54		553		-		607
Direct lending funds		-		-		37		37
Other debt obligations		-		16		-		16


Pledged assets for Zion decommissioning subtotal(c)		89		599		37		725

Rabbi trust investments
Cash equivalents		2		-		-		2
Mutual funds(d)		-		34		-		34

Rabbi trust investments subtotal		2		34		-		36

Commodity mark-to-market derivative assets
Cash flow hedges		-		857		-		857
Other derivatives		-		1,653		124		1,777
Proprietary trading		-		240		48		288
Interest rate mark-to-market derivative assets		-		15		-		15
Effect of netting and allocation of collateral(e)		-		(1,827)		(28)		(1,855)

Mark-to-market assets(f)		-		938		144		1,082

Total assets		3,505		5,569		194		9,268

Liabilities
Commodity mark-to-market derivative liabilities
Cash flow hedges		-		(13)		-		(13)
Other derivatives		(1)		(1,137)		(119)		(1,257)
Proprietary trading		-		(236)		(28)		(264)
Interest rate mark-to-market derivative liabilities		-		(19)		-		(19)
Effect of netting and allocation of collateral(e)		-		1,295		20		1,315

Mark-to-market liabilities(f)		(1)		(110)		(127)		(238)

Deferred compensation		-		(73)		-		(73)

Total liabilities		(1)		(183)		(127)		(311)

Total net assets	$	3,504	$	5,386	$	67	$	8,957

As of December 31, 2010	Level 1		Level 2		Level 3		Total
Assets
Cash equivalents(a)	$	1,473	$	-	$	-	$	1,473
Nuclear decommissioning trust fund investments
Cash equivalents		45		-		-		45
Equity
Equity securities		1,513		-		-		1,513
Commingled funds		-		2,081		-		2,081
Equity funds subtotal		1,513		2,081		-		3,594
Fixed income
Debt securities issued by the U.S. Treasury and other
U.S. government corporations and agencies		504		96		-		600
Debt securities issued by states of the United States
and political subdivisions of the states		-		451		-		451
Corporate debt securities		-		619		-		619
Federal agency mortgage-backed securities		-		804		-		804
Commercial mortgage-backed securities (non-agency)		-		114		-		114
Residential mortgage-backed securities (non-agency)		-		14		-		14
Commingled funds		-		47		-		47
Mutual funds		-		40		-		40
Fixed income subtotal		504		2,185		-		2,689
Other debt obligations		-		48		-		48

Nuclear decommissioning trust fund investments
subtotal(b)		2,062		4,314		-		6,376

Pledged assets for Zion decommissioning
Equity
Equity securities		84		-		-		84
Commingled funds		-		82		-		82
Equity funds subtotal		84		82		-		166
Fixed income
Debt securities issued by the U.S. Treasury and other
U.S. government corporations and agencies		166		12		-		178
Debt securities issued by states of the United States
and political subdivisions of the states		-		45		-		45
Corporate debt securities		-		263		-		263
Federal agency mortgage-backed securities		-		102		-		102
Commercial mortgage-backed securities (non-agency)		-		14		-		14
Commingled funds		-		50		-		50
Fixed income subtotal		166		486		-		652
Other debt obligations		-		2		-		2
Pledged assets for Zion decommissioning
subtotal(c)		250		570		-		820

Rabbi trust investments
Mutual funds(d)		-		36		-		36

Rabbi trust investments subtotal		-		36		-		36

Mark-to-market derivative assets
Cash flow hedges		-		724		12		736
Other derivatives		2		1,709		57		1,768
Proprietary trading		-		235		46		281
Effect of netting and allocation of collateral(e)		(3)		(1,848)		(38)		(1,889)
Mark-to-market assets(f)		(1)		820		77		896

Total assets		3,784		5,740		77		9,601

Liabilities
Mark-to-market derivative liabilities
Cash flow hedges		-		(45)		-		(45)
Other derivatives		(2)		(667)		(29)		(698)
Proprietary trading		-		(233)		(21)		(254)
Effect of netting and allocation of collateral(e)		1		914		23		938
Mark-to-market liabilities(f)		(1)		(31)		(27)		(59)
Deferred compensation		-		(76)		-		(76)

Total liabilities		(1)		(107)		(27)		(135)

Total net assets	$	3,783	$	5,633	$	50	$	9,466

(a) Excludes certain cash equivalents considered to be held-to-maturity and not reported at fair value.

(b) Excludes net (liabilities) assets of $(57) million and $32 million at December 31, 2011 and 2010, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables and payables related to pending securities purchases.

(c) Excludes net assets of $9 million and $4 million at December 31, 2011 and 2010. These items consist of receivables related to pending securities sales, interest and dividend receivables and payables related to pending securities purchases.

(d) Excludes $25 million of the cash surrender value of life insurance investments at December 31, 2011 and 2010.

(e) Includes collateral postings received from counterparties. Collateral received from counterparties, net of collateral paid to counterparties, totaled $532 million and $8 million allocated to Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2011. Collateral received from counterparties, net of collateral paid to counterparties, totaled $2 million, $934 million and $15 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2010.

(f) The Level 3 balance does not include current and noncurrent assets for Generation and current and noncurrent liabilities for ComEd of $503 million and $191 million at December 31, 2011 and $450 million and $525 million at December 31, 2010, respectively, related to the fair value of Generation's financial swap contract with ComEd; and current assets of $5 million at December 31, 2010, related to the fair value of Generation's block contracts with PECO, which eliminate upon consolidation in Exelon's Consolidated Financial Statements. Generation's block contracts with PECO ended December 31, 2011.

Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis

For the Year Ended December 31, 2011		Nuclear Decommissioning Trust Fund Investment		Pledged Assets for Zion Station Decommissioning				Mark-to-Market Derivatives		Total
Balance as of January 1, 2011		$	-	$	-		$	50		$	50
Total realized / unrealized gains (losses)
	Included in income		1		-			99	(a)		100
	Included in other comprehensive income		-		-			(25)	(b)		(25)
	Included in regulatory liabilities		2		-			(106)			(104)
Change in collateral			-		-			6			6
Purchases, sales, issuances and settlements
	Purchases		10		60			10			80
	Sales		-		(23)			-			(23)
Transfers out of Level 3			-		-			(17)			(17)

Balance as of December 31, 2011		$	13	$	37	-	$	17		$	67
The amount of total gains included in income
	attributed to the change in unrealized gains related to assets and liabilities held for the year ended December 31, 2011	$	1	$	-		$	131		$	132

(a) Includes the reclassification of $32 million of realized losses due to settlements of derivative contracts recorded in results of operations for the year ended December 31, 2011.

(b) Excludes $170 million of increases in fair value and $451 million of realized losses reclassified from OCI due to settlements of associated with Generation's financial swap contract with ComEd for the year ended December 31, 2011 and $5 million of decreases in fair value due to settlement of Generation's block contracts with PECO for the year ended December 31, 2011. All items eliminate upon consolidation in Exelon's Consolidated Financial Statements.

For the Year Ended December 31, 2010		Servicing Liability			Nuclear Decommissioning Trust Fund Investments		Mark-to-Market Derivatives			Total
Balance as of January 1, 2010		$	(2)		$	-	$	(44)		$	(46)
Total realized / unrealized gains
	Included in income		2	(c)		-		46	(a)		48
	Included in other comprehensive income		-			-		16	(b )		16
	Included in regulatory assets/liabilities		-			-		2			2
Change in collateral			-			-		(10)			(10)
Purchases, sales, issuances and settlements
	Purchases		-			13		15			28
	Sales		-			(1)		-			(1)
Transfers out of Level 3			-			(12)		25			13

Balance as of December 31, 2010		$	-		$	-	$	50		$	50
The amount of total gains included in income
	attributed to the change in unrealized gains related to assets and liabilities held for the year ended December 31, 2010	$	-		$	-	$	54		$	54

(a) Includes the reclassification of $8 million of realized losses due to settlements of derivative contracts recorded in results of operations.

(b) Excludes increases in fair value of $375 million and realized losses reclassified from OCI due to settlements of $371 million associated with Generation's financial swap contract with ComEd for the year ended December 31, 2010. The PECO block contracts were designated as normal sales as of May 31, 2010. As such, there were no effective changes in the fair value of the block contracts with PECO after that point, as the mark-to-market balances previously recorded will be amortized over the term of the contracts. The increase in fair value was $3 million through May 31, 2010. Generation's block contracts with PECO ended December 31, 2011. All items eliminate upon consolidation in Exelon's Consolidated Financial Statements.

(c) The servicing liability related to PECO's accounts receivable agreement was released in accordance with new guidance on accounting for transfers of financial assets that was adopted on January 1, 2010. See Note 10 - Debt and Credit Agreements for additional information.

Total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis

		Operating Revenue		Purchased Power		Fuel		Other, net (a)
Total gains (losses) included in income for the year ended
	December 31, 2011	$	108	$	-	$	(9)	$	1
Change in the unrealized gains (losses) relating to assets and
	liabilities held for the year ended December 31, 2011	$	137	$	-	$	(6)	$	1

		Operating Revenue		Purchased Power		Fuel		Other, net
Total gains included in income for the year ended
	December 31, 2010	$	3	$	7	$	36	$	-
Change in the unrealized gains relating to assets and liabilities
	held for the year ended December 31, 2010	$	22	$	4	$	28	$	-

Other, net activity consists of realized and unrealized gains included in income for the NDT funds held by Generation.

Exelon Generation Co L L C [Member]

Fair Value Tables [Line Items]

Fair value of financial liabilities recorded at the carrying amount

	2011				2010
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt (including amounts due within one year)	$	3,677	$	4,231	$	3,679	$	3,792
Spent nuclear fuel obligation		1,019		886		1,018		876

Assets and liabilities measured and recorded at fair value on recurring basis

As of December 31, 2011	Level 1		Level 2		Level 3			Total
Assets
Cash equivalents(a)	$	466	$	-	$	-	$	466
Nuclear decommissioning trust fund investments
Cash equivalents		504		-		-		504
Equity
Equity securities		1,275		-		-		1,275
Commingled funds		-		1,822		-		1,822
Equity funds subtotal		1,275		1,822		-		3,097
Fixed income
Debt securities issued by the U.S. Treasury and other U.S.
government corporations and agencies		774		345		-		1,119
Debt securities issued by states of the United States and
political subdivisions of the states		-		541		-		541
Corporate debt securities		-		779		-		779
Federal agency mortgage-backed securities		-		357		-		357
Commercial mortgage-backed securities (non-agency)		-		83		-		83
Residential mortgage-backed securities (non-agency)		-		5		-		5
Mutual funds		-		47		-		47
Fixed income subtotal		774		2,157		-		2,931
Other debt obligations		-		19		13		32
Nuclear decommissioning trust fund investments subtotal(b)		2,553		3,998		13		6,564

Pledged assets for Zion Station decommissioning
Equity
Equity securities		35		-		-		35
Commingled funds		-		30		-		30
Equity funds subtotal		35		30		-		65
Fixed income
Debt securities issued by the U.S. Treasury and other U.S.
government corporations and agencies		54		26		-		80
Debt securities issued by states of the United States and
political subdivisions of the states		-		65		-		65
Corporate debt securities		-		311		-		311
Federal agency mortgage-backed securities		-		121		-		121
Commercial mortgage-backed securities (non-agency)		-		10		-		10
Commingled funds		-		20				20
Fixed income subtotal		54		553		-		607
Direct lending funds		-		-		37		37
Other debt obligations		-		16		-		16
Pledged assets for Zion Station decommissioning subtotal(c)		89		599		37		725
Rabbi trust investments(d)(e)		-		4		-		4
Commodity mark-to-market derivative assets
Cash flow hedges		-		857		694		1,551
Other derivatives		-		1,653		124		1,777
Proprietary trading		-		240		48		288
Effect of netting and allocation of collateral(f)		-		(1,827)		(28)		(1,855)
Mark-to-market assets(g)		-		923		838		1,761
									.
Total assets		3,108		5,524		888		9,520

Liabilities
Commodity mark-to-market derivative liabilities
Cash flow hedges		-		(13)		-		(13)
Other derivatives		(1)		(1,137)		(13)		(1,151)
Proprietary trading		-		(236)		(28)		(264)
Interest rate mark-to-market derivative liabilities		-		(19)		-		(19)
Effect of netting and allocation of collateral(f)		-		1,295		20		1,315
Mark-to-market liabilities		(1)		(110)		(21)		(132)
Deferred compensation		-		(18)		-		(18)

Total liabilities		(1)		(128)		(21)		(150)

Total net assets	$	3,107	$	5,396	$	867	$	9,370

As of December 31, 2010	Level 1		Level 2		Level 3			Total
Assets
Cash equivalents(a)	$	419	$	-	$	-	$	419
Nuclear decommissioning trust fund investments
Cash equivalents		45		-		-		45
Equity
Equity securities		1,513		-		-		1,513
Commingled funds		-		2,081		-		2,081
Equity funds subtotal		1,513		2,081		-		3,594
Fixed income
Debt securities issued by the U.S. Treasury and other U.S.
government corporations and agencies		504		96		-		600
Debt securities issued by states of the United States and
political subdivisions of the states		-		451		-		451
Corporate debt securities		-		619		-		619
Federal agency mortgage-backed securities		-		804		-		804
Commercial mortgage-backed securities (non-agency)		-		114		-		114
Residential mortgage-backed securities (non-agency)		-		14		-		14
Commingled funds		-		47		-		47
Mutual funds		-		40		-		40
Fixed income subtotal		504		2,185		-		2,689
Other debt obligations		-		48		-		48
Nuclear decommissioning trust fund investments subtotal(b)		2,062		4,314		-		6,376

Pledged assets for Zion Station decommissioning
Equity
Equity securities		84		-		-		84
Commingled funds		-		82		-		82
Equity funds subtotal		84		82		-		166
Fixed income
Debt securities issued by the U.S. Treasury and other U.S.
government corporations and agencies		166		12		-		178
Debt securities issued by states of the United States and
political subdivisions of the states		-		45		-		45
Corporate debt securities		-		263		-		263
Federal agency mortgage-backed securities		-		102		-		102
Commercial mortgage-backed securities (non-agency)		-		14		-		14
Residential mortgage-backed securities (non-agency)		-		-		-		-
Commingled funds		-		50		-		50
Fixed income subtotal		166		486		-		652
Other debt obligations		-		2		-		2
Pledged assets for Zion Station decommissioning
subtotal(c)		250		570		-		820
Rabbi trust investments(d)(e)		-		4		-		4
Mark-to-market derivative assets
Cash flow hedges		-		724		992		1,716
Other derivatives		2		1,695		53		1,750
Proprietary trading		-		235		46		281
Effect of netting and allocation of collateral(f)		(3)		(1,848)		(38)		(1,889)
Mark-to-market derivative net assets(g)		(1)		806		1,053		1,858

Total assets		2,730		5,694		1,053		9,477

Liabilities
Mark-to-market derivative liabilities
Cash flow hedges		-		(45)		-		(45)
Other derivatives		(2)		(667)		(25)		(694)
Proprietary trading		-		(233)		(21)		(254)
Effect of netting and allocation of collateral(f)		1		914		23		938
Mark-to-market liabilities		(1)		(31)		(23)		(55)
Deferred compensation		-		(20)		-		(20)

Total liabilities		(1)		(51)		(23)		(75)

Total net assets	$	2,729	$	5,643	$	1,030	$	9,402

__________

(a) Excludes certain cash equivalents considered to be held-to-maturity and not reported at fair value.

(b) Excludes net (liabilities) assets of $(57) million and $32 million at December 31, 2011 and 2010, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.

(c) Excludes net assets of $9 million and $4 million at December 31, 2011 and 2010, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.

(d) The mutual funds held by the Rabbi trusts that are invested in common stock of Standard and Poor's 500 companies and Pennsylvania municipal bonds are primarily rated as investment grade.

(e) Excludes $7 million of the cash surrender value of life insurance investments at December 31, 2011 and 2010.

(f) Includes collateral postings received from counterparties. Collateral received from counterparties, net of collateral paid to counterparties, totaled $532 million and $8 million allocated to Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2011. Collateral received from counterparties, net of collateral paid to counterparties, totaled $2 million, $934 million and $15 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2010.

(g) The Level 3 balance includes current and noncurrent assets for Generation of $503 million and $191 million at December 31, 2011 and $450 million and $525 million at December 31, 2010, respectively, related to the fair value of Generation's financial swap contract with ComEd; and current assets of $5 million at December 31, 2010 related to the fair value of Generation's block contracts with PECO. All of the mark-to-market balances Generation carries associated with the financial swap contract with ComEd and the block contracts with PECO eliminate upon consolidation in Exelon's Consolidated Financial Statements. Generation's block contracts with PECO ended December 31, 2011.

Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis

Year Ended December 31, 2011		Nuclear Decommissioning Trust Fund Investments			Pledged Assets for Zion Station Decommissioning	Mark-to-Market Derivatives			Total
Balance as of January 1, 2011		$	-		-	$	1,030		$	1,030
Total unrealized / realized gains (losses)
	Included in income		1		-		99	(a)		100
	Included in other comprehensive income		-		-		(311)	(b)		(311)
	Included in noncurrent payables to affiliates		2		-		-			2
Change in collateral			-		-		6			6
Purchases, sales, issuances and settlements
	Purchases		10		60		10			80
	Sales		-		(23)		-			(23)
Transfers out of Level 3			-		-		(17)			(17)

Balance as of December 31, 2011		$	13		37	$	817		$	867
The amount of total gains included in income attributed
	to the change in unrealized gains related to assets and liabilities held for the year ended December 31, 2011	$	1	$	-	$	131		$	132

Year Ended December 31, 2010		Nuclear Decommissioning Trust Fund Investments		Mark-to-Market Derivatives			Total
Balance as of January 1, 2010		$	-	$	931		$	931
Total unrealized / realized gains:
	Included in income		-		46	(a)		46
	Included in other comprehensive income		-		23	(b)		23
Change in collateral			-		(10)			(10)
Purchases, sales, issuances and settlements:
	Purchases		13		15			28
	Sales		(1)		-			(1)
Transfers out of Level 3			(12)		25			13

Balance as of December 31, 2010		$	-	$	1,030		$	1,030
The amount of total gains included in income attributed
	to the change in unrealized gains related to assets and liabilities held for the year ended December 31, 2010	$	-	$	54		$	54

(a) Includes the reclassification of $8 million of realized losses due to settlements of derivative contracts recorded in results of operations.

(b) Includes increases in fair value of $375 million and realized losses reclassified from OCI due to settlements of $371 million associated with Generation's financial swap contract with ComEd for the year ended December 31, 2010. 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 after that point, as the mark-to-market balances previously recorded will be amortized over the term of the contracts. The increase in fair value was $3 million through May 31, 2010. All items eliminate upon consolidation in Exelon's Consolidated Financial Statements.

Total realized and unrealized gains (losses) included in income for Level 3 assets and liabilities measured at fair value on a recurring basis

		Operating Revenue		Purchased Power		Fuel		Other, net (a)
Total gains (losses) included in income for the year ended
	December 31, 2011	$	108	$	-	$	(9)	$	1
Change in the unrealized gains (losses) relating to assets and liabilities
	held for the year ended December 31, 2011	$	137	$	-	$	(6)	$	1

		Operating Revenue		Purchased Power		Fuel		Other, net
Total gains included in income for the year ended
	December 31, 2010	$	3	$	7	$	36	$	-
Change in the unrealized gains relating to assets and liabilities held for
	the year ended December 31, 2010	$	22	$	4	$	28	$	-

Commonwealth Edison Co [Member]

Fair Value Tables [Line Items]

Fair value of financial liabilities recorded at the carrying amount

	2011				2010
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt (including amounts due within one year)	$	5,665	$	6,540	$	5,001	$	5,411
Long-term debt to financing trust		206		184		206		176

Assets and liabilities measured and recorded at fair value on recurring basis

As of December 31, 2011		Level 1		Level 2		Level 3		Total
Assets
Cash equivalents(a)		$	173	$	-	$	-	$	173
Rabbi trust investments
Cash equivalents			2		-		-		2
Mutual funds			-		19		-		19
Rabbi trust investments subtotal			2		19		-		21

Total assets			175		19		-		194

Liabilities
Deferred compensation obligation			-		(8)		-		(8)
Mark-to-market derivative liabilities(b)(c)			-		-		(800)		(800)

Total liabilities			-		(8)		(800)		(808)

Total net assets (liabilities)		$	175	$	11	$	(800)	$	(614)

As of December 31, 2010		Level 1		Level 2		Level 3		Total
Assets
Cash equivalents(a)		$	1	$	-	$	-	$	1
Rabbi trust investments
	Mutual Funds		-		23		-		23

Rabbi trust investments subtotal			-		23		-		23
Mark-to-market derivative assets (c)			-		-		4		4

Total assets			1		23		4		28

Liabilities
Deferred compensation obligation			-		(8)		-		(8)
Mark-to-market derivative liabilities(b)			-		-		(975)		(975)

Total liabilities			-		(8)		(975)		(983)

Total net assets (liabilities)		$	1	$	15	$	(971)	$	(955)

(a) Excludes certain cash equivalents considered to be held-to-maturity and not reported at fair value.

(b) The Level 3 balance includes a current and noncurrent liability of $503 million and $191 million at December 31, 2011, respectively, and $450 million and $525 million at December 31, 2010, respectively, related to the fair value of ComEd's financial swap contract with Generation which eliminates upon consolidation in Exelon's Consolidated Financial Statements.

(c) The Level 3 balance includes a current and noncurrent liability of $9 million and $ 97 million at December 31, 2011, respectively, and a noncurrent asset of $4 million at December 31, 2010 related to floating-to-fixed energy swap contracts with unaffiliated suppliers.

Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis

For the Year Ended December 31, 2011	Mark-to-Market Derivatives
Balance as of January 1, 2011	$	(971)
Total realized / unrealized gains / (losses) included in regulatory assets(a)(b)		171

Balance as of December 31, 2011	$	(800)

(a) Includes decreases in fair value of $170 million and realized gains due to settlements of $451 million associated with ComEd's financial swap contract with Generation. All items eliminated upon consolidated in Exelon's Consolidated Financial Statements.

(b) Includes a decrease in fair value of $110 million associated with floating-to-fixed energy swap contracts with unaffiliated suppliers.

For the Year Ended December 31, 2010	Mark-to-Market Derivatives
Balance as of January 1, 2010	$	(971)
Total realized / unrealized gains / (losses) included in regulatory assets(a)(b)		0

Balance as of December 31, 2010	$	(971)

Includes decreases in fair value of $375 million and realized gains due to settlements of $371 million associated with ComEd's financial swap contract with Generation. All items eliminated upon consolidation in Exelon's Consolidated Financial Statements.
Includes an increase in fair value of $4 million associated with floating-to-fixed energy swap contracts with unaffiliated suppliers.

PECO Energy Co [Member]

Fair Value Tables [Line Items]

Fair value of financial liabilities recorded at the carrying amount

	2011				2010
	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term debt (including amounts due within one year)	$	1,972	$	2,295	$	2,222	$	2,402
Long-term debt to financing trusts		184		174		184		173
Preferred securities		87		79		87		68

Assets and liabilities measured and recorded at fair value on recurring basis

December 31, 2011	Level 1		Level 2		Level 3		Total
Assets
Cash equivalents(a)	$	175	$	-	$	-	$	175
Rabbi trust investments - mutual funds(b)		-		9		-		9

Total assets		175		9		-		184

Liabilities
Deferred compensation obligation		-		(21)		-		(21)
Current mark-to-market derivative liabilities(c)		-		-		-		-

Total liabilities		-		(21)		-		(21)

Total net assets (liabilities)	$	175	$	(12)	$	-	$	163

As of December 31, 2010	Level 1		Level 2		Level 3		Total
Assets
Cash equivalents(a)	$	499	$	-	$	-	$	499
Rabbi trust investments - mutual funds(b)		-		7		-		7

Total assets		499		7		-		506

Liabilities
Deferred compensation obligation		-		(23)		-		(23)
Noncurrent mark-to-market derivative liabilities(c)		-		-		(9)		(9)

Total liabilities		-		(23)		(9)		(32)

Total net assets (liabilities)	$	499	$	(16)	$	(9)	$	474

(a) Excludes certain cash equivalents considered to be held-to-maturity and not reported at fair value.

(b) Excludes $13 million of the cash surrender value of life insurance investments at December 31, 2011 and 2010.

(c) The Level 3 balances include a current liability of $5 million at the December 31, 2010, related to the fair value of PECO's block contracts with Generation that eliminate upon consolidation in Exelon's Consolidated Financial Statements. Generation's block contracts with PECO expired on December 31, 2011.

Fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis

For the Year Ended December 31, 2011	Mark-to-Market Derivatives
Balance as of January 1, 2011	$	(9)
Total realized/unrealized gains included in regulatory assets (a)		9

Balance as of December 31, 2011	$	-

(a) Includes an increase of $5 million related to the settlement of PECO's block contracts with Generation, which eliminates upon consolidation in Exelon's Consolidated Financial Statements. Generation's block contracts with PECO expired on December 31, 2011.

For the Year Ended December 31, 2010		Mark-to-Market Derivatives			Servicing Liability			Total
Balance as of January 1, 2010		$	(4)		$	(2)		$	(6)
	Total realized/unrealized gains (losses):
	Included in net income		-			2	(a)		2
	Included in regulatory assets		(5)	(b)		-			(5)

Balance as of December 31, 2010		$	(9)		$	-		$	(9)

- Definition

Tabular disclosure of the total amount of gains or losses for the period which are included in earnings or resulted in a change to net assets which gains or losses have arisen from the use of significant unobservable inputs (Level 3) to measure the fair value of assets and liabilities. Such gains or losses are attributable to the change in unrealized gains or losses relating to those assets and liabilities so valued which are still held at the reporting date and which change are also considered for disclosure; it may be expected that a description of where those unrealized gains or losses are reported in the statement of income or the statement of financial position would also be disclosed.

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- Definition

Tabular disclosure of the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments, assets, and liabilities. Such certain disclosures about the financial instruments, assets, and liabilities include: (1) the fair value of the required items together with their carrying amounts (as appropriate) and (2) the methodology and assumptions used in developing such estimates of fair value.

+ References

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