Fair Value of Financial Assets and Liabilities (Fair Value Measurements, Recurring and Nonrecurring) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	$ 1,230	[1]	$ 995	[1]
Fixed income [Abstract]
Proprietary trading	(328)
Interest rate mark-to-market Subtotal			50
Other investments	15
Deferred compensation	(114)
Total assets	11,162		10,785
Total liabilities	(573)
Total net assets	10,589		10,050
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	114
Mark-to-market derivative liabilities (current liabilities)	159		352
Mark-to-market derivative liabilities (noncurrent liabilities)	300		281
Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	459		245
Equity Securities [Abstract]
Equity securities	1,776		1,480
Exchange traded funds	115
Commingled funds	2,271		1,933
Equity securities subtotal	4,162		3,413
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	882		1,057
Debt securities issued by states of the United States and political subdivisions of the states	294		321
Debt securities issued by foreign governments	87		93
Corporate debt securities	1,784		1,788
Federal agency mortgage-backed securities	10		24
Commercial mortgage-backed securities (non-agency)	40		45
Residential mortgage-backed securities (non-agency)	7		11
Mutual funds fixed income	18		23
Fixed income subtotal	3,122		3,362
Private equity	5
Direct lending securities	314		183
Other debt obligations	14		15
Nuclear decommissioning trust fund investments subtotal	8,076	[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	(5)		30
Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	26		23
Equity Securities [Abstract]
Equity securities	16		14
Commingled funds			9
Equity securities subtotal	16		23
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	49		130
Debt securities issued by states of the United States and political subdivisions of the states	20		37
Corporate debt securities	227		249
Federal agency mortgage-backed securities			49
Commercial mortgage-backed securities (non-agency)			6
Fixed income subtotal	296		471
Direct lending securities	112		89
Other debt obligations			1
Pledged assets for Zion Station decommissioning subtotal	451	[3]	607	[3]
Rabbi trust investments subtotal			71
Other derivatives	1
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from pledged assets	7		7
Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	2		2
Fixed income [Abstract]
Mutual funds	54	[4]	69	[4]
Rabbi trust investments subtotal	56
Deferred compensation	(53)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	53
Supplemental executive retirement plan fair value	1
Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Other investments			19
Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation			(102)
Total liabilities			(735)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation			102
Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	3,960		4,675
Proprietary trading	1,761		3,193
Effect of netting and allocation of collateral received/(paid)	(4,424)	[5]	(6,056)	[5]
Mark-to-market subtotal	1,297	[6]	1,812	[6]
Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(3,020)		(3,566)
Proprietary trading	(1,703)		(3,121)
Effect of netting and allocation of collateral received/(paid)	4,280	[7]	6,087	[5]
Mark-to-market subtotal	(443)	[6]	(600)	[6]
Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	32		51
Interest rate mark to market	69		114
Interest rate mark-to-market Subtotal	37		63
Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(32)		(51)
Interest rate mark to market	(48)		(84)
Interest rate mark-to-market Subtotal	(16)		(33)
Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	1,230	[1]
Fixed income [Abstract]
Total liabilities	1
Total net assets	4,534		3,979
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties	6
Fair Value Inputs Level 1 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	459		245
Equity Securities [Abstract]
Equity securities	1,776		1,480
Exchange traded funds	115
Equity securities subtotal	1,891		1,480
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	882		1,057
Fixed income subtotal	882		1,057
Nuclear decommissioning trust fund investments subtotal	3,232	[2]	2,782	[2]
Pledged assets for Zion Station decommissioning subtotal			132	[3]
Fair Value Inputs Level 1 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	16		14
Equity securities subtotal	16		14
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	45		118
Fixed income subtotal	45		118
Pledged assets for Zion Station decommissioning subtotal	61	[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	54	[4]	69	[4]
Rabbi trust investments subtotal	56		71
Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents			995	[1]
Fixed income [Abstract]
Other investments	0		2
Total assets	4,533		4,062
Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Total liabilities			(83)
Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	493
Proprietary trading	324		1,042
Effect of netting and allocation of collateral received/(paid)	(863)	[5]	(1,823)	[5]
Mark-to-market subtotal	(46)	[6]	80	[6]
Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(540)		(1,041)
Proprietary trading	(328)		(1,084)
Effect of netting and allocation of collateral received/(paid)	869	[7]	2,042	[5]
Mark-to-market subtotal	1	[6]	(83)	[6]
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)	30
Interest rate mark to market	30
Interest rate mark-to-market Subtotal	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)	(31)
Interest rate mark to market	(31)
Fair Value Inputs Level 2 [Member]
Fixed income [Abstract]
Total assets	5,575
Total liabilities	(269)
Total net assets	5,306		5,415
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties	(124)		(155)
Fair Value Inputs Level 2 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Equity Securities [Abstract]
Commingled funds	2,271		1,933
Equity securities subtotal	2,271		1,933
Fixed income [Abstract]
Debt securities issued by states of the United States and political subdivisions of the states	294		321
Debt securities issued by foreign governments	87		93
Corporate debt securities	1,753		1,788
Federal agency mortgage-backed securities	10		24
Commercial mortgage-backed securities (non-agency)	40		45
Residential mortgage-backed securities (non-agency)	7		11
Mutual funds fixed income	18		23
Fixed income subtotal	2,209		2,305
Other debt obligations	14		15
Nuclear decommissioning trust fund investments subtotal	4,494	[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	26		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	4		12
Debt securities issued by states of the United States and political subdivisions of the states	20		37
Corporate debt securities	227		249
Federal agency mortgage-backed securities			49
Commercial mortgage-backed securities (non-agency)			6
Fixed income subtotal	251		353
Other debt obligations	1		1
Pledged assets for Zion Station decommissioning subtotal	278	[3]	386	[3]
Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Total assets			5,778
Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	(114)		(102)
Total liabilities			(363)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	114		102
Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	2,582		3,173
Proprietary trading	1,315		2,078
Effect of netting and allocation of collateral received/(paid)	(3,131)	[5]	(4,175)	[5]
Mark-to-market subtotal	766	[6]	1,076	[6]
Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(1,890)		(2,289)
Proprietary trading	(1,256)		(1,959)
Effect of netting and allocation of collateral received/(paid)	3,007	[7]	4,020	[5]
Mark-to-market subtotal	(139)	[6]	(228)	[6]
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)	2		51
Interest rate mark to market	39		114
Interest rate mark-to-market Subtotal	37		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	(17)		(84)
Interest rate mark-to-market Subtotal	(16)		(33)
Fair Value Inputs Level 3 [Member]
Fixed income [Abstract]
Total liabilities	(305)
Total net assets	749		656
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties	(26)		(33)
Fair Value Inputs Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fixed income [Abstract]
Corporate debt securities	31
Private equity	5
Direct lending securities	314		183
Nuclear decommissioning trust fund investments subtotal	350	[2]	183	[2]
Fair Value Inputs Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fixed income [Abstract]
Fixed income subtotal	0
Direct lending securities	112		89
Pledged assets for Zion Station decommissioning subtotal	112	[3]	89	[3]
Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Other investments	15		17
Total assets	1,054		945
Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Total liabilities			(289)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Fair value of energy swap contract current liability	17		18
Fair value of energy swap contract noncurrent liability	176		49
Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	885		641
Proprietary trading	122		73
Effect of netting and allocation of collateral received/(paid)	(430)	[5]	(58)	[5]
Mark-to-market subtotal	577	[6]	656	[6]
Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(590)		(236)
Proprietary trading	(119)		(78)
Effect of netting and allocation of collateral received/(paid)	404	[7]	25	[5]
Mark-to-market subtotal	(305)	[6]	(289)	[6]
Exelon Generation Co L L C [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	1,006
Fixed income [Abstract]
Other investments	15
Total assets	10,888
Total net assets	10,597		9,839
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)	142		334
Mark-to-market derivative liabilities (noncurrent liabilities)	120		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	459		245
Equity Securities [Abstract]
Equity securities	1,776		1,480
Exchange traded funds	115
Commingled funds	2,271		1,933
Equity securities subtotal	4,162		3,413
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	882		1,057
Debt securities issued by states of the United States and political subdivisions of the states	294		321
Debt securities issued by foreign governments	87		93
Corporate debt securities	1,784		1,788
Federal agency mortgage-backed securities	10		24
Commercial mortgage-backed securities (non-agency)	40		45
Residential mortgage-backed securities (non-agency)	7		11
Mutual funds fixed income	18		23
Fixed income subtotal	3,122		3,362
Private equity	5
Direct lending securities	314		183
Other debt obligations	14		15
Nuclear decommissioning trust fund investments subtotal	8,076	[2],[3]	7,218	[2]
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	26		23
Equity Securities [Abstract]
Equity securities	16		14
Commingled funds			9
Equity securities subtotal	16		23
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	49		130
Debt securities issued by states of the United States and political subdivisions of the states	20		37
Corporate debt securities	227		249
Federal agency mortgage-backed securities			49
Commingled funds fixed income			6
Fixed income subtotal	296		471
Direct lending securities	112		89
Other debt obligations	1		1
Pledged assets for Zion Station decommissioning subtotal	451	[3]	607	[3]
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	[8]	13	[4],[8]
Rabbi trust investments subtotal	13		14
Exelon Generation Co L L C [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents			487	[1]
Fixed income [Abstract]
Other investments			19
Total assets			10,433
Exelon Generation Co L L C [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	(29)		(28)
Total liabilities	(291)		(594)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	29		28
Exelon Generation Co L L C [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Cash flow hedges			4,901
Other derivatives	3,960
Proprietary trading	1,761		3,193
Effect of netting and allocation of collateral received/(paid)	(4,424)	[6]	(6,056)	[7]
Mark-to-market subtotal	1,297		2,038	[6]
Exelon Generation Co L L C [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges			(3,499)
Other derivatives	(2,827)
Proprietary trading	(1,703)		(3,121)
Effect of netting and allocation of collateral received/(paid)	4,280	[6]	6,087	[5]
Mark-to-market subtotal	(250)		(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)	32		51
Interest rate mark to market	62		101
Interest rate mark-to-market Subtotal	30		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)	(32)		(51)
Interest rate mark to market	(44)		(84)
Interest rate mark-to-market Subtotal	(12)		(33)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member]
Fixed income [Abstract]
Total net assets	4,267		3,414
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	459		245
Equity Securities [Abstract]
Equity securities	1,776		1,480
Exchange traded funds	115
Commingled funds	0
Equity securities subtotal	1,891		1,480
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	882		1,057
Fixed income subtotal	882		1,057
Nuclear decommissioning trust fund investments subtotal	3,232	[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	16		14
Equity securities subtotal	16		14
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	45		118
Fixed income subtotal	45		118
Pledged assets for Zion Station decommissioning subtotal	61	[3]	132	[3]
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	[8]	13	[4],[8]
Rabbi trust investments subtotal	13		14
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	1,006		487	[1]
Fixed income [Abstract]
Other investments	0		2
Total assets	4,266		3,497
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	0
Total liabilities	1		(83)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Cash flow hedges			861
Other derivatives	493
Proprietary trading	324		1,042
Effect of netting and allocation of collateral received/(paid)	(863)	[6]	(1,823)	[7]
Mark-to-market subtotal	(46)		80	[6]
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			(1,041)
Other derivatives	(540)
Proprietary trading			(1,084)
Effect of netting and allocation of collateral received/(paid)	869	[6]	2,042	[5]
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)	30
Interest rate mark to market	30
Interest rate mark-to-market Subtotal	0
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)	(31)
Interest rate mark to market	(31)
Interest rate mark-to-market Subtotal	0
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member]
Fixed income [Abstract]
Total net assets	5,388		5,476
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Equity Securities [Abstract]
Commingled funds	2,271		1,933
Equity securities subtotal	2,271		1,933
Fixed income [Abstract]
Debt securities issued by states of the United States and political subdivisions of the states	294		321
Debt securities issued by foreign governments	87		93
Corporate debt securities	1,753		1,788
Federal agency mortgage-backed securities	10		24
Commercial mortgage-backed securities (non-agency)	40		45
Residential mortgage-backed securities (non-agency)	7		11
Mutual funds fixed income	18		23
Fixed income subtotal	2,209		2,305
Other debt obligations	14		15
Nuclear decommissioning trust fund investments subtotal	4,494	[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	26		23
Equity Securities [Abstract]
Commingled funds			9
Equity securities subtotal	0		9
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	4		12
Debt securities issued by states of the United States and political subdivisions of the states	20		37
Corporate debt securities	227		249
Federal agency mortgage-backed securities			49
Commingled funds fixed income			6
Fixed income subtotal	251		353
Other debt obligations	1		1
Pledged assets for Zion Station decommissioning subtotal	278	[3]	386	[3]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Other investments	0
Total assets	5,568		5,765
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	(29)		(28)
Total liabilities	(180)		(289)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	29		28
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Cash flow hedges			3,173
Other derivatives	2,582
Proprietary trading	1,315		2,078
Effect of netting and allocation of collateral received/(paid)	(3,131)	[6]	(4,175)	[7]
Mark-to-market subtotal	766		1,076	[6]
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			(2,289)
Other derivatives	(1,890)
Proprietary trading	(1,256)		(1,959)
Effect of netting and allocation of collateral received/(paid)	3,007	[6]	4,020	[5]
Mark-to-market subtotal	(139)		(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)	2		51
Interest rate mark to market	32		101
Interest rate mark-to-market Subtotal	30
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	(13)		(84)
Interest rate mark-to-market Subtotal	(12)		(33)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member]
Fixed income [Abstract]
Total net assets	942		949
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fixed income [Abstract]
Private equity	5
Direct lending securities	314		183
Nuclear decommissioning trust fund investments subtotal	350	[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]
Fixed income subtotal	0
Direct lending securities	112		89
Pledged assets for Zion Station decommissioning subtotal	112	[3]	89	[3]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Other investments	15		17
Total assets	1,054		1,171
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	0
Total liabilities	(112)		(222)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Cash flow hedges			867
Other derivatives	885
Proprietary trading	122		73
Effect of netting and allocation of collateral received/(paid)	(430)	[6]	(58)	[7]
Mark-to-market subtotal	577		882	[6]
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			(169)
Other derivatives	(397)
Proprietary trading	(119)		(78)
Effect of netting and allocation of collateral received/(paid)	404	[6]	25	[5]
Mark-to-market subtotal	(112)		(222)
Commonwealth Edison Co [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)	17		18
Mark-to-market derivative liabilities (noncurrent liabilities)	176		49
Commonwealth Edison Co [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	(5)		(8)
Rabbi trust investments subtotal	(5)		(8)
Commonwealth Edison Co [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		(111)
Fixed income [Abstract]
Total assets	(5)		(119)
Commonwealth Edison Co [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	193	[9]	293	[10],[9]
Deferred compensation	8		8
Total liabilities	201		301
Total net assets	196		182
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(8)		(8)
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	(5)		(8)
Rabbi trust investments subtotal	(5)		(8)
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		(111)
Fixed income [Abstract]
Total assets	(5)		(119)
Total net assets	(5)		(119)
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal			293	[10],[9]
Deferred compensation	8		8
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 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Total liabilities	193		293
Total net assets	193		293
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	193	[9]
PECO Energy Co [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal			9
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)	0		0
Mark-to-market derivative liabilities (noncurrent liabilities)	0		0
PECO Energy Co [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	(9)	[11]
PECO Energy Co [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	(175)		(346)
Fixed income [Abstract]
Rabbi trust investments subtotal			(9)	[11]
Total assets	(184)		(355)
Total net assets	(167)		(337)
PECO Energy Co [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	(17)		(18)
Total liabilities	(17)		(18)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	17		18
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal			9
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	(9)	[11]	(9)	[11]
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	(175)		(346)
Fixed income [Abstract]
Total assets	(184)		(355)
Total net assets	(184)		(355)
PECO Energy Co [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	(17)		(18)
Total liabilities	(17)		(18)
Total net assets	17		18
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	17		18
Baltimore Gas and Electric Company [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	6		5
Baltimore Gas and Electric Company [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	6
Baltimore Gas and Electric Company [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	31		33
Fixed income [Abstract]
Rabbi trust investments subtotal			5
Total assets	37		38
Total net assets	31		33
Baltimore Gas and Electric Company [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	(6)		(5)
Total liabilities	(6)		(5)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	6		5
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	6		5
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	6
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	31		33
Fixed income [Abstract]
Rabbi trust investments subtotal			5
Total assets	37		38
Total net assets	37		38
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	(6)
Total liabilities	(6)		(5)
Total net assets	(6)		(5)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	6
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Deferred compensation			(5)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation			$ 5

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

[2] Excludes net assets (liabilities) of $(5) million and $30 million at December 31, 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 assets of $7 million at both December 31, 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 $53 million related to deferred compensation and $1 million related to Supplemental Executive Retirement Plan at December 31, 2013, and $53 million related to deferred compensation and $16 million related to Supplemental Executive Retirement Plan at December 31, 2012.

[5] Excludes $32 million and $28 million of the cash surrender value of life insurance investments at December 31, 2013 and December 31, 2012, respectively.

[6] The Level 3 balance does not include current assets for Generation and current liabilities for ComEd of $226 million at December 31, 2012 related to the fair value of Generation's financial swap contract with ComEd.

[7] Includes collateral postings (received) from counterparties. Collateral (received) from counterparties, net of collateral paid to counterparties, totaled $6 million, $(124) million and $(26) million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 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.

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

[9] 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 eliminates upon consolidation in Exelon's Consolidated Financial Statements.

[10] The Level 3 balance includes the current and noncurrent liability of $17 million and $176 million at December 31, 2013, respectively, and $18 million and $49 million at December 31, 2012, respectively, related to floating-to-fixed energy swap contracts with unaffiliated suppliers.

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