Fair Value of Financial Assets and Liabilities (Fair Value Measurements, Recurring and Nonrecurring) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	$ 589	[1]	$ 995	[1]
Fixed income [Abstract]
Other investments	12		19
Deferred compensation	(105)		(102)
Total assets	10,294		10,785
Total liabilities	(430)		(735)
Total net assets	9,864		10,050
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	105		102
Mark-to-market derivative liabilities (current liabilities)	147		352
Mark-to-market derivative liabilities (noncurrent liabilities)	178		281
Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	229		245
Equity Securities [Abstract]
Equity securities	1,691		1,480
Commingled funds	2,071		1,933
Equity securities subtotal	3,762		3,413
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	966		1,057
Debt securities issued by states of the United States and political subdivisions of the states	314		321
Debt securities issued by foreign governments	85		93
Corporate debt securities	1,727		1,788
Federal agency mortgage-backed securities	18		24
Commercial mortgage-backed securities (non-agency)	41		45
Residential mortgage-backed securities (non-agency)	10		11
Mutual funds fixed income	37		23
Fixed income subtotal	3,198		3,362
Direct lending securities	240		183
Other debt obligations	12		15
Nuclear decommissioning trust fund investments subtotal	7,441	[2]	7,218	[2]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	22		30
Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	62		23
Equity Securities [Abstract]
Equity securities	1		14
Commingled funds			9
Equity securities subtotal	1		23
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	151		130
Debt securities issued by states of the United States and political subdivisions of the states	27		37
Corporate debt securities	193		249
Federal agency mortgage-backed securities	17		49
Commercial mortgage-backed securities (non-agency)	1		6
Fixed income subtotal	389		471
Direct lending securities	111		89
Other debt obligations	3		1
Pledged assets for Zion Station decommissioning subtotal	566	[3]	607	[3]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from pledged assets	(28)		7
Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	2		2
Equity Securities [Abstract]
Equity securities subtotal	0
Fixed income [Abstract]
Mutual funds	67	[4],[5]	69	[4],[5]
Rabbi trust investments subtotal	69		71
Deferred compensation	(51)		(53)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	51		53
Supplemental executive retirement plan fair value	16		16
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	29		28
Derivative Financial Instruments Liabilities [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair value of energy swap contract current liability	16		18
Fair value of energy swap contract noncurrent liability	69		49
Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	4,056		4,675
Proprietary trading	2,446		3,193
Effect of netting and allocation of collateral received/(paid)	(4,958)	[6]	(6,056)	[6]
Mark-to-market subtotal	1,544		1,812	[7]
Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(3,227)		(3,566)
Proprietary trading	(2,367)		(3,121)
Effect of netting and allocation of collateral received/(paid)	5,286	[6]	6,087	[6]
Mark-to-market subtotal	(308)	[7]	(600)	[7]
Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(37)		51
Interest rate mark to market	110		114
Interest rate mark-to-market Subtotal	73		63
Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(37)		51
Interest rate mark to market	(54)		84
Interest rate mark-to-market Subtotal	(17)		33
Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	589	[1]	995	[1]
Fixed income [Abstract]
Other investments	1		2
Deferred compensation	0		0
Total assets	3,604		4,062
Total liabilities	1		(83)
Total net assets	3,605		3,979
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Collateral received from counterparties, net of collateral paid to counterparties	188		219
Fair Value Inputs Level 1 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	229		245
Equity Securities [Abstract]
Equity securities	1,691		1,480
Commingled funds	0
Equity securities subtotal	1,691		1,480
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	966		1,057
Debt securities issued by states of the United States and political subdivisions of the states	0
Debt securities issued by foreign governments	0
Corporate debt securities	0
Federal agency mortgage-backed securities	0
Commercial mortgage-backed securities (non-agency)	0
Residential mortgage-backed securities (non-agency)	0
Mutual funds fixed income	0
Fixed income subtotal	966		1,057
Direct lending securities	0
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	2,886	[2]	2,782	[2]
Fair Value Inputs Level 1 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	1		14
Equity securities subtotal	1		14
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	143		118
Debt securities issued by states of the United States and political subdivisions of the states	0
Corporate debt securities	0
Federal agency mortgage-backed securities	0
Fixed income subtotal	143		118
Direct lending securities	0
Pledged assets for Zion Station decommissioning subtotal	144	[3]	132	[3]
Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	2		2
Fixed income [Abstract]
Mutual funds	67	[4],[5]	69	[4],[5]
Rabbi trust investments subtotal	69		71
Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	721		861
Proprietary trading	839		1,042
Effect of netting and allocation of collateral received/(paid)	(1,645)	[6]	(1,823)	[6]
Mark-to-market subtotal			80	[7]
Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(977)		(1,041)
Proprietary trading	(855)		(1,084)
Effect of netting and allocation of collateral received/(paid)	1,833	[6]	2,042	[6]
Mark-to-market subtotal	1	[7]	(83)	[7]
Fair Value Inputs Level 1 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(36)
Mark-to-market subtotal	(85)
Interest rate mark to market	36
Interest rate mark-to-market Subtotal	0		0
Fair Value Inputs Level 1 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	36
Interest rate mark to market	(36)
Interest rate mark-to-market Subtotal	0		0
Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0	[1]	0	[1]
Fixed income [Abstract]
Deferred compensation	(105)		(102)
Total assets	5,716		5,778
Total liabilities	(250)		(363)
Total net assets	5,466		5,415
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	105		102
Collateral received from counterparties, net of collateral paid to counterparties	130		(155)
Fair Value Inputs Level 2 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0
Equity Securities [Abstract]
Equity securities	0
Commingled funds	2,071		1,933
Equity securities subtotal	2,071		1,933
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0
Debt securities issued by states of the United States and political subdivisions of the states	314		321
Debt securities issued by foreign governments	85		93
Corporate debt securities	1,727		1,788
Federal agency mortgage-backed securities	18		24
Commercial mortgage-backed securities (non-agency)	41		45
Residential mortgage-backed securities (non-agency)	10		11
Mutual funds fixed income	37		23
Fixed income subtotal	2,232		2,305
Direct lending securities	0
Other debt obligations	12		15
Nuclear decommissioning trust fund investments subtotal	4,315	[2]	4,253	[2]
Fair Value Inputs Level 2 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	62		23
Equity Securities [Abstract]
Commingled funds			9
Equity securities subtotal			9
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	8		12
Debt securities issued by states of the United States and political subdivisions of the states	27		37
Corporate debt securities	193		249
Federal agency mortgage-backed securities	17		49
Commercial mortgage-backed securities (non-agency)	1		6
Fixed income subtotal	246		353
Direct lending securities	0
Other debt obligations	3		1
Pledged assets for Zion Station decommissioning subtotal	311	[3]	386	[3]
Fair Value Inputs Level 2 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0
Fixed income [Abstract]
Mutual funds	0	[4],[5]
Rabbi trust investments subtotal	0		0
Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Other investments	0
Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	2,659		3,173
Proprietary trading	1,445		2,078
Effect of netting and allocation of collateral received/(paid)	(3,087)	[6]	(4,175)	[6]
Mark-to-market subtotal	1,017		1,076	[7]
Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(1,974)		(2,289)
Proprietary trading	(1,371)		(1,959)
Effect of netting and allocation of collateral received/(paid)	3,217	[6]	4,020	[6]
Mark-to-market subtotal	(128)	[7]	(228)	[7]
Fair Value Inputs Level 2 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(1)		51
Interest rate mark to market	74		114
Interest rate mark-to-market Subtotal	73		63
Fair Value Inputs Level 2 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(1)		(51)
Interest rate mark to market	(18)		84
Interest rate mark-to-market Subtotal	(17)		33
Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0	[1]	0	[1]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	236	[6]
Other investments	11		17
Deferred compensation	0		0
Total assets	974		945
Total liabilities	(181)		(289)
Total net assets	793		656
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Collateral received from counterparties, net of collateral paid to counterparties	10		(33)
Fair Value Inputs Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0
Equity Securities [Abstract]
Equity securities	0		0
Commingled funds	0
Equity securities subtotal	0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0
Debt securities issued by states of the United States and political subdivisions of the states	0
Debt securities issued by foreign governments	0
Corporate debt securities	0
Federal agency mortgage-backed securities	0
Commercial mortgage-backed securities (non-agency)	0
Residential mortgage-backed securities (non-agency)	0
Mutual funds fixed income	0
Fixed income subtotal	0		0
Direct lending securities	240		183
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	240	[2]	183	[2]
Fair Value Inputs Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities subtotal			0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0
Debt securities issued by states of the United States and political subdivisions of the states	0
Corporate debt securities	0
Federal agency mortgage-backed securities	0
Fixed income subtotal	0		0
Direct lending securities	111		89
Pledged assets for Zion Station decommissioning subtotal	111	[3]	89	[3]
Fair Value Inputs Level 3 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0
Fixed income [Abstract]
Mutual funds	0	[4],[5]
Rabbi trust investments subtotal	0		0
Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	676		641
Proprietary trading	162		73
Effect of netting and allocation of collateral received/(paid)	(226)	[6]	(58)	[6]
Mark-to-market subtotal	612		656	[7]
Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(276)		(236)
Proprietary trading	(141)		(78)
Effect of netting and allocation of collateral received/(paid)			25	[6]
Mark-to-market subtotal	(181)	[7]	(289)	[7]
Fair Value Inputs Level 3 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Interest rate mark to market	0
Interest rate mark-to-market Subtotal	0		0
Fair Value Inputs Level 3 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Interest rate mark to market	0
Interest rate mark-to-market Subtotal	0		0
Exelon Generation Co L L C [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	45		487	[1]
Fixed income [Abstract]
Other investments	12		19
Deferred compensation	(25)		(28)
Total assets	9,662		10,433
Total liabilities	(265)		(594)
Total net assets	9,397		9,839
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	25		28
Mark-to-market derivative liabilities (current liabilities)	131		334
Mark-to-market derivative liabilities (noncurrent liabilities)	109		232
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	229		245
Equity Securities [Abstract]
Equity securities	1,691		1,480
Commingled funds	2,071		1,933
Equity securities subtotal	3,762		3,413
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	966		1,057
Debt securities issued by states of the United States and political subdivisions of the states	314		321
Debt securities issued by foreign governments	85		93
Corporate debt securities	1,727		1,788
Federal agency mortgage-backed securities	18		24
Commercial mortgage-backed securities (non-agency)	41		45
Residential mortgage-backed securities (non-agency)	10		11
Mutual funds fixed income	37		23
Fixed income subtotal	3,198		3,362
Direct lending securities	240		183
Other debt obligations	12		15
Nuclear decommissioning trust fund investments subtotal	7,441	[2]	7,218	[2]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	22		30
Exelon Generation Co L L C [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	62		23
Equity Securities [Abstract]
Equity securities	1		14
Commingled funds			9
Equity securities subtotal	1		23
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	151		130
Debt securities issued by states of the United States and political subdivisions of the states	27		37
Corporate debt securities	193		249
Federal agency mortgage-backed securities	17		49
Commercial mortgage-backed securities (non-agency)	1		6
Commingled funds fixed income			0
Fixed income subtotal	389		471
Direct lending securities	111		89
Other debt obligations	3		1
Pledged assets for Zion Station decommissioning subtotal	566	[8]	607	[8]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	(28)		7
Exelon Generation Co L L C [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		1
Fixed income [Abstract]
Mutual funds	13	[10],[9]	13	[10],[9]
Rabbi trust investments subtotal	13		14
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	9		8
Exelon Generation Co L L C [Member] | Derivative Financial Instruments Assets [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair value swap contract current asset	0		226
Fair value swap contract noncurrent asset	0		0
Exelon Generation Co L L C [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	4,056		4,901
Proprietary trading	2,446		3,193
Effect of netting and allocation of collateral received/(paid)	(4,958)	[6]	(6,056)	[6]
Mark-to-market subtotal	1,544		2,038	[11]
Exelon Generation Co L L C [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges	0
Other derivatives	(3,142)		(3,499)
Proprietary trading	(2,367)		(3,121)
Effect of netting and allocation of collateral received/(paid)	5,286	[6]	6,087	[6]
Mark-to-market subtotal	(223)		(533)
Exelon Generation Co L L C [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	37		51
Interest rate mark to market	78		101
Interest rate mark-to-market Subtotal	41		50
Exelon Generation Co L L C [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(37)		(51)
Interest rate mark to market	(54)		(84)
Interest rate mark-to-market Subtotal	(17)		(33)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	45		487	[1]
Fixed income [Abstract]
Other investments	1		2
Deferred compensation	0
Total assets	3,004		3,497
Total liabilities	1		(83)
Total net assets	3,005		3,414
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0
Collateral received from counterparties, net of collateral paid to counterparties	188				219
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	229		245
Equity Securities [Abstract]
Equity securities	1,691		1,480
Commingled funds	0
Equity securities subtotal	1,691		1,480
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	966		1,057
Debt securities issued by states of the United States and political subdivisions of the states	0
Fixed income subtotal	966		1,057
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	2,886	[2]	2,782	[2]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	1		14
Equity securities subtotal	1		14
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	143		118
Fixed income subtotal	143		118
Pledged assets for Zion Station decommissioning subtotal	144	[8]	132	[8]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		1
Fixed income [Abstract]
Mutual funds	13	[10],[9]	13	[10],[9]
Rabbi trust investments subtotal	13		14
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	721		861
Proprietary trading	839		1,042
Effect of netting and allocation of collateral received/(paid)	(1,645)	[6]	(1,823)	[6]
Mark-to-market subtotal	(85)		80	[11]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges	0
Other derivatives	(977)		(1,041)
Proprietary trading	(855)		(1,084)
Effect of netting and allocation of collateral received/(paid)	1,833	[6]	2,042	[6]
Mark-to-market subtotal	1		(83)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	36
Interest rate mark to market	36
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(36)
Interest rate mark to market	(36)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0	[1]
Fixed income [Abstract]
Deferred compensation	(25)		(28)
Total assets	5,684		5,765
Total liabilities	(170)		(289)
Total net assets	5,514		5,476
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	25		28
Collateral received from counterparties, net of collateral paid to counterparties	130				(155)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0
Equity Securities [Abstract]
Equity securities	0
Commingled funds	2,071		1,933
Equity securities subtotal	2,071		1,933
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0
Debt securities issued by states of the United States and political subdivisions of the states	314		321
Debt securities issued by foreign governments	85		93
Corporate debt securities	1,727		1,788
Federal agency mortgage-backed securities	18		24
Commercial mortgage-backed securities (non-agency)	41		45
Residential mortgage-backed securities (non-agency)	10		11
Mutual funds fixed income	37		23
Fixed income subtotal	2,232		2,305
Other debt obligations	12		15
Nuclear decommissioning trust fund investments subtotal	4,315	[2]	4,253	[2]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	62		23
Equity Securities [Abstract]
Commingled funds			9
Equity securities subtotal			9
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	8		12
Debt securities issued by states of the United States and political subdivisions of the states	27		37
Corporate debt securities	193		249
Federal agency mortgage-backed securities	17		49
Commercial mortgage-backed securities (non-agency)	1		6
Commingled funds fixed income			0
Fixed income subtotal	246		353
Direct lending securities	0
Other debt obligations	3		1
Pledged assets for Zion Station decommissioning subtotal	311	[8]	386	[8]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal			0
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	2,659		3,173
Proprietary trading	1,445		2,078
Effect of netting and allocation of collateral received/(paid)	(3,087)	[6]	(4,175)	[6]
Mark-to-market subtotal	1,017		1,076	[11]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges	0
Other derivatives	(1,974)		(2,289)
Proprietary trading	(1,371)		(1,959)
Effect of netting and allocation of collateral received/(paid)	3,217	[6]	4,020	[6]
Mark-to-market subtotal	(128)		(228)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	1		51
Interest rate mark to market	42		101
Interest rate mark-to-market Subtotal	41		50
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(1)		(51)
Interest rate mark to market	(18)		(84)
Interest rate mark-to-market Subtotal	(17)		(33)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		0	[1]
Equity Securities [Abstract]
Equity securities	0
Fixed income [Abstract]
Other investments	11		17
Deferred compensation	0
Total assets	974		1,171
Total liabilities	(96)		(222)
Total net assets	878		949
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0
Collateral received from counterparties, net of collateral paid to counterparties	10				(33)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Equity Securities [Abstract]
Commingled funds	0
Equity securities subtotal	0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0
Debt securities issued by states of the United States and political subdivisions of the states	0
Mutual funds fixed income	0
Fixed income subtotal	0
Direct lending securities	240		183
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	240	[2]	183	[2]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fixed income [Abstract]
Direct lending securities	111		89
Pledged assets for Zion Station decommissioning subtotal	111	[8]	89	[8]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal			0
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	676		867
Proprietary trading	162		73
Effect of netting and allocation of collateral received/(paid)	(226)	[6]	(58)	[6]
Mark-to-market subtotal	612		882	[11]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges	0
Other derivatives	(191)		(169)
Proprietary trading	(141)		(78)
Effect of netting and allocation of collateral received/(paid)	236	[6]	25	[6]
Mark-to-market subtotal	(96)		(222)
Commonwealth Edison Co [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	70		111	[9]
Fixed income [Abstract]
Deferred compensation	(8)		(8)
Total assets	76		119
Total liabilities	(93)		(301)
Total net assets	(17)		(182)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	8		8
Mark-to-market derivative liabilities (current liabilities)	16		18
Mark-to-market derivative liabilities (noncurrent liabilities)	69		49
Commonwealth Edison Co [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	6		8
Rabbi trust investments subtotal	6		8
Commonwealth Edison Co [Member] | Derivative Financial Instruments Assets [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair value swap contract current asset	0		226
Fair value swap contract noncurrent asset	0		0
Commonwealth Edison Co [Member] | Derivative Financial Instruments Liabilities [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair value of energy swap contract current liability	16		18
Fair value of energy swap contract noncurrent liability	69		49
Commonwealth Edison Co [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	85	[12],[7]	293	[12],[7]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	70		111	[9]
Fixed income [Abstract]
Deferred compensation	0
Total assets	76		119
Total liabilities	0		0
Total net assets	76		119
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	6		8
Rabbi trust investments subtotal	6		8
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	0	[12],[7]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0
Fixed income [Abstract]
Deferred compensation	(8)		(8)
Total assets	0		0
Total liabilities	(8)		(8)
Total net assets	(8)		(8)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	8		8
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	0
Rabbi trust investments subtotal	0		0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	0	[12],[7]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0
Fixed income [Abstract]
Deferred compensation	0
Total assets	0		0
Total liabilities	(85)		(293)
Total net assets	(85)		(293)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	0
Rabbi trust investments subtotal	0		0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	85	[12],[7]	293	[12],[7]
PECO Energy Co [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	13		346
Fixed income [Abstract]
Deferred compensation	(16)		(18)
Total assets	22		355
Total liabilities	(16)		(18)
Total net assets	6		337
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	16		18
PECO Energy Co [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	9		9
Rabbi trust investments subtotal	9	[13],[14]	9	[13],[14]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	14		13
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	13		346
Fixed income [Abstract]
Total assets	22		355
Total net assets	22		355
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	9		9
Rabbi trust investments subtotal	9	[13],[14]	9	[13],[14]
PECO Energy Co [Member] | Fair Value Inputs Level 2 [Member]
Fixed income [Abstract]
Deferred compensation	(16)		(18)
Total liabilities	(16)		(18)
Total net assets	(16)		(18)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	16		18
PECO Energy Co [Member] | Fair Value Inputs Level 2 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds			0
PECO Energy Co [Member] | Fair Value Inputs Level 3 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds			0
Baltimore Gas and Electric Company [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	365		33
Fixed income [Abstract]
Deferred compensation	(5)		(5)
Total assets	370		38
Total liabilities	(5)		(5)
Total net assets	365		33
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	5		5
Baltimore Gas and Electric Company [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	5	[13]	5	[13]
Rabbi trust investments subtotal	5		5
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	365		33
Fixed income [Abstract]
Total assets	370		38
Total net assets	370		38
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	5	[13]	5	[13]
Rabbi trust investments subtotal	5		5
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 2 [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	0
Deferred compensation	(5)		(5)
Total assets	0
Total liabilities	(5)		(5)
Total net assets	(5)		(5)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	5		5
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 2 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	0
Rabbi trust investments subtotal	0
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 3 [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	0
Total assets	0
Total net assets	0
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 3 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	0
Rabbi trust investments subtotal	$ 0

[1] Excludes certain cash equivalents considered to be held-to-maturity and not reported at fair value.

[2] Excludes net assets of $22 million and $30 million at June 30, 2013 and December 31, 2012, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.

[3] Excludes net (liabilities) assets of $ (28) million and $7 million at June 30, 2013 and December 31, 2012, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.

[4] The mutual funds held by the Rabbi trusts include $51 million related to deferred compensation and $16 million related to Supplemental Executive Retirement Plan at June 30, 2013, and $53 million related to deferred compensation and $16 million related to Supplemental Executive Retirement Plan at December 31, 2012. These funds are classified as Level 1 as they are valued based upon quoted prices (unadjusted) in active markets.

[5] Excludes $29 million and $28 million of the cash surrender value of life insurance investments at June 30, 2013 and December 31, 2012, respectively.

[6] Includes collateral postings (received) from counterparties. Collateral (received) from counterparties, net of collateral paid to counterparties, totaled $188 million, $130 million and $10 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of June 30, 2013. Collateral (received) from counterparties, net of collateral paid to counterparties, totaled $219 million, $(155) million and $(33) million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2012.

[7] The Level 3 balance includes the current and noncurrent liability of $16 million and $69 million at June 30, 2013, respectively, and $18 million and $49 million at December 31, 2012, respectively, related to floating-to-fixed energy swap contracts with unaffiliated suppliers.

[8] Excludes net (liabilities) assets of $ (28) million and $7 million at June 30, 2013 December 31, 2012, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.

[9] The mutual funds held by the Rabbi trusts are classified as Level 1 as they are valued based upon quoted prices (unadjusted) in active markets.

[10] Excludes $9 million and $8 million of the cash surrender value of life insurance investments at June 30, 2013 and December 31, 2012, respectively.

[11] The level 3 balance includes current assets for Generation of $226 million at December 31, 2012, related to the fair value of Generation’s financial swap contract with ComEd, which eliminates upon consolidation in Exelon’s Consolidated Financial Statements.

[12] The Level 3 balance includes the current liability of $226 million at December 31, 2012, related to the fair value of ComEd's financial swap contract with Generation which eliminated upon consolidation in Exelon's Consolidated Financial Statements.

[13] Excludes $14 million and $13 million of the cash surrender value of life insurance investments at June 30, 2013 and December 31, 2012, respectively.

[14]