Fair Value of Financial Assets and Liabilities (Fair Value Measurements, Recurring and Nonrecurring) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	$ 1	[1]	$ 995	[1]
Fixed income [Abstract]
Other investments	12		19
Deferred compensation	(108)		(102)
Total assets	9,815		10,785
Total liabilities	(452)		(735)
Total net assets	9,363		10,050
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	108		102
Mark-to-market derivative liabilities (current liabilities)	126		352
Mark-to-market derivative liabilities (noncurrent liabilities)	218		281
Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	558		245
Equity Securities [Abstract]
Equity securities	1,600		1,480
Exchange traded funds	110
Commingled funds	2,114		1,933
Equity securities subtotal	3,824		3,413
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	938		1,057
Debt securities issued by states of the United States and political subdivisions of the states	295		321
Debt securities issued by foreign governments	84		93
Corporate debt securities	1,712		1,788
Federal agency mortgage-backed securities	16		24
Commercial mortgage-backed securities (non-agency)	41		45
Residential mortgage-backed securities (non-agency)	7		11
Mutual funds fixed income	29		23
Fixed income subtotal	3,122		3,362
Direct lending securities	245		183
Other debt obligations	14		15
Nuclear decommissioning trust fund investments subtotal	7,763	[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	13		30
Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	25		23
Equity Securities [Abstract]
Equity securities	4		14
Commingled funds			9
Equity securities subtotal	4		23
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	96		130
Debt securities issued by states of the United States and political subdivisions of the states	24		37
Corporate debt securities	217		249
Federal agency mortgage-backed securities	7		49
Commercial mortgage-backed securities (non-agency)			6
Fixed income subtotal	344		471
Direct lending securities	106		89
Other debt obligations			1
Pledged assets for Zion Station decommissioning subtotal	479	[3]	607	[3]
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
Equity Securities [Abstract]
Equity securities subtotal	0
Fixed income [Abstract]
Mutual funds	49	[4],[5]	69	[4],[5]
Rabbi trust investments subtotal	51		71
Deferred compensation	(49)		(53)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	49		53
Supplemental executive retirement plan fair value	0		16
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	30		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	106		49
Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	3,784		4,675
Proprietary trading	2,024		3,193
Effect of netting and allocation of collateral received/(paid)	(4,347)	[6]	(6,056)	[6]
Mark-to-market subtotal	1,461		1,812	[7]
Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(2,845)		(3,566)
Proprietary trading	(1,976)		(3,121)
Effect of netting and allocation of collateral received/(paid)	4,493	[6]	6,087	[6]
Mark-to-market subtotal	(328)	[7]	(600)	[7]
Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(35)		51
Interest rate mark to market	83		114
Interest rate mark-to-market Subtotal	48		63
Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(35)		51
Interest rate mark to market	(51)		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	[1]	995	[1]
Fixed income [Abstract]
Other investments	1		2
Deferred compensation	0		0
Total assets	3,308		4,062
Total liabilities	(92)		(83)
Total net assets	3,216		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	108		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	558		245
Equity Securities [Abstract]
Equity securities	1,600		1,480
Exchange traded funds	110
Commingled funds	0
Equity securities subtotal	1,710		1,480
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	938		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	938		1,057
Direct lending securities	0
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	3,206	[2]	2,782	[2]
Fair Value Inputs Level 1 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	4		14
Equity securities subtotal	4		14
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	89		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	89		118
Direct lending securities	0
Pledged assets for Zion Station decommissioning subtotal	93	[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	49	[4],[5]	69	[4],[5]
Rabbi trust investments subtotal	51		71
Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	540		861
Proprietary trading	666		1,042
Effect of netting and allocation of collateral received/(paid)	(1,251)	[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	(764)		(1,041)
Proprietary trading	(686)		(1,084)
Effect of netting and allocation of collateral received/(paid)	1,359	[6]	2,042	[6]
Mark-to-market subtotal	(91)	[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)	(33)
Mark-to-market subtotal	(45)
Interest rate mark to market	34
Interest rate mark-to-market Subtotal	1		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)	33
Interest rate mark to market	(34)
Interest rate mark-to-market Subtotal	(1)		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	(108)		(102)
Total assets	5,579		5,778
Total liabilities	(133)		(363)
Total net assets	5,446		5,415
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	108		102
Collateral received from counterparties, net of collateral paid to counterparties	58		(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	2,114		1,933
Equity securities subtotal	2,114		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	295		321
Debt securities issued by foreign governments	84		93
Corporate debt securities	1,712		1,788
Federal agency mortgage-backed securities	16		24
Commercial mortgage-backed securities (non-agency)	41		45
Residential mortgage-backed securities (non-agency)	7		11
Mutual funds fixed income	29		23
Fixed income subtotal	2,184		2,305
Direct lending securities	0
Other debt obligations	14		15
Nuclear decommissioning trust fund investments subtotal	4,312	[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	25		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	7		12
Debt securities issued by states of the United States and political subdivisions of the states	24		37
Corporate debt securities	217		249
Federal agency mortgage-backed securities	7		49
Commercial mortgage-backed securities (non-agency)			6
Fixed income subtotal	255		353
Direct lending securities	0
Other debt obligations			1
Pledged assets for Zion Station decommissioning subtotal	280	[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	2,541		3,173
Proprietary trading	1,184		2,078
Effect of netting and allocation of collateral received/(paid)	(2,785)	[6]	(4,175)	[6]
Mark-to-market subtotal	940		1,076	[7]
Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(1,718)		(2,289)
Proprietary trading	(1,135)		(1,959)
Effect of netting and allocation of collateral received/(paid)	2,843	[6]	4,020	[6]
Mark-to-market subtotal	(10)	[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)	(2)		51
Interest rate mark to market	49		114
Interest rate mark-to-market Subtotal	47		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)	(2)		(51)
Interest rate mark to market	(17)		84
Interest rate mark-to-market Subtotal	(15)		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)	291	[6]
Other investments	11		17
Deferred compensation	0		0
Total assets	928		945
Total liabilities	(227)		(289)
Total net assets	701		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	(20)		(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	245		183
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	245	[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	106		89
Pledged assets for Zion Station decommissioning subtotal	106	[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	703		641
Proprietary trading	174		73
Effect of netting and allocation of collateral received/(paid)	(311)	[6]	(58)	[6]
Mark-to-market subtotal	566		656	[7]
Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(363)		(236)
Proprietary trading	(155)		(78)
Effect of netting and allocation of collateral received/(paid)			25	[6]
Mark-to-market subtotal	(227)	[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	674		487	[1]
Fixed income [Abstract]
Other investments	12		19
Deferred compensation	(27)		(28)
Total assets	10,436		10,433
Total liabilities	(249)		(594)
Total net assets	10,187		9,839
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	27		28
Mark-to-market derivative liabilities (current liabilities)	110		334
Mark-to-market derivative liabilities (noncurrent liabilities)	112		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	558		245
Equity Securities [Abstract]
Equity securities	1,600		1,480
Exchange traded funds	110
Commingled funds	2,114		1,933
Equity securities subtotal	3,824		3,413
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	938		1,057
Debt securities issued by states of the United States and political subdivisions of the states	295		321
Debt securities issued by foreign governments	84		93
Corporate debt securities	1,712		1,788
Federal agency mortgage-backed securities	16		24
Commercial mortgage-backed securities (non-agency)	41		45
Residential mortgage-backed securities (non-agency)	7		11
Mutual funds fixed income	29		23
Fixed income subtotal	3,122		3,362
Direct lending securities	245		183
Other debt obligations	14		15
Nuclear decommissioning trust fund investments subtotal	7,763	[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	13		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	25		23
Equity Securities [Abstract]
Equity securities	4		14
Commingled funds			9
Equity securities subtotal	4		23
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	96		130
Debt securities issued by states of the United States and political subdivisions of the states	24		37
Corporate debt securities	217		249
Federal agency mortgage-backed securities	7		49
Commercial mortgage-backed securities (non-agency)			6
Fixed income subtotal	344		471
Direct lending securities	106		89
Other debt obligations			1
Pledged assets for Zion Station decommissioning subtotal	479	[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	7		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	12	[9]	13	[9]
Rabbi trust investments subtotal	12		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	3,784		4,901
Proprietary trading	2,024		3,193
Effect of netting and allocation of collateral received/(paid)	(4,347)	[6]	(6,056)	[6]
Mark-to-market subtotal	1,461		2,038	[10]
Exelon Generation Co L L C [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges	0
Other derivatives	(2,723)		(3,499)
Proprietary trading	(1,976)		(3,121)
Effect of netting and allocation of collateral received/(paid)	4,493	[6]	6,087	[6]
Mark-to-market subtotal	(206)		(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)	35		51
Interest rate mark to market	70		101
Interest rate mark-to-market Subtotal	35		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)	(35)		(51)
Interest rate mark to market	(51)		(84)
Interest rate mark-to-market Subtotal	(16)		(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	674		487	[1]
Fixed income [Abstract]
Other investments	1		2
Deferred compensation	0
Total assets	3,942		3,497
Total liabilities	(92)		(83)
Total net assets	3,850		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	108				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	558		245
Equity Securities [Abstract]
Equity securities	1,600		1,480
Exchange traded funds	110
Commingled funds	0
Equity securities subtotal	1,710		1,480
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	938		1,057
Debt securities issued by states of the United States and political subdivisions of the states	0
Fixed income subtotal	938		1,057
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	3,206	[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	4		14
Equity securities subtotal	4		14
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	89		118
Fixed income subtotal	89		118
Pledged assets for Zion Station decommissioning subtotal	93	[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	12	[9]	13	[9]
Rabbi trust investments subtotal	12		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	540		861
Proprietary trading	666		1,042
Effect of netting and allocation of collateral received/(paid)	(1,251)	[6]	(1,823)	[6]
Mark-to-market subtotal	(45)		80	[10],[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	(764)		(1,041)
Proprietary trading	(686)		(1,084)
Effect of netting and allocation of collateral received/(paid)	1,359	[6]	2,042	[6]
Mark-to-market subtotal	(91)		(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)	33
Interest rate mark to market	34
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)	(33)
Interest rate mark to market	(34)
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	(27)		(28)
Total assets	5,566		5,765
Total liabilities	(52)		(289)
Total net assets	5,514		5,476
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	27		28
Collateral received from counterparties, net of collateral paid to counterparties	58				(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	2,114		1,933
Equity securities subtotal	2,114		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	295		321
Debt securities issued by foreign governments	84		93
Corporate debt securities	1,712		1,788
Federal agency mortgage-backed securities	16		24
Commercial mortgage-backed securities (non-agency)	41		45
Residential mortgage-backed securities (non-agency)	7		11
Mutual funds fixed income	29		23
Fixed income subtotal	2,184		2,305
Other debt obligations	14		15
Nuclear decommissioning trust fund investments subtotal	4,312	[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	25		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	7		12
Debt securities issued by states of the United States and political subdivisions of the states	24		37
Corporate debt securities	217		249
Federal agency mortgage-backed securities	7		49
Commercial mortgage-backed securities (non-agency)			6
Fixed income subtotal	255		353
Direct lending securities	0
Other debt obligations			1
Pledged assets for Zion Station decommissioning subtotal	280	[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	2,541		3,173
Proprietary trading	1,184		2,078
Effect of netting and allocation of collateral received/(paid)	(2,785)	[6]	(4,175)	[6]
Mark-to-market subtotal	940		1,076	[10]
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	(1,718)		(2,289)
Proprietary trading	(1,135)		(1,959)
Effect of netting and allocation of collateral received/(paid)	2,843	[6]	4,020	[6]
Mark-to-market subtotal	(10)		(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	36		101
Interest rate mark-to-market Subtotal	34		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)	(2)		(51)
Interest rate mark to market	(17)		(84)
Interest rate mark-to-market Subtotal	(15)		(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	928		1,171
Total liabilities	(105)		(222)
Total net assets	823		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	(20)				(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	245		183
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	245	[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	106		89
Pledged assets for Zion Station decommissioning subtotal	106	[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	703		867
Proprietary trading	174		73
Effect of netting and allocation of collateral received/(paid)	(311)	[6]	(58)	[11],[6]
Mark-to-market subtotal	566		882	[10],[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	(241)		(169)
Proprietary trading	(155)		(78)
Effect of netting and allocation of collateral received/(paid)	291	[6]	25	[6]
Mark-to-market subtotal	(105)		(222)
Commonwealth Edison Co [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		111
Fixed income [Abstract]
Deferred compensation	(8)		(8)
Total assets	5		119
Total liabilities	(130)		(301)
Total net assets	(125)		(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)	106		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]
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	106		49
Commonwealth Edison Co [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	122	[11],[7]	293	[11],[7]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0		111
Fixed income [Abstract]
Deferred compensation	0
Total assets	5		119
Total liabilities	0		0
Total net assets	5		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	5		8
Rabbi trust investments subtotal	5		8
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	0	[11],[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	[11],[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	(122)		(293)
Total net assets	(122)		(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	122	[11],[7]	293	[11],[7]
PECO Energy Co [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	583		346
Fixed income [Abstract]
Deferred compensation	(16)		(18)
Total assets	592		355
Total liabilities	(16)		(18)
Total net assets	576		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	[12],[13]	9	[12],[13]
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	583		346
Fixed income [Abstract]
Total assets	592		355
Total net assets	592		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	[12],[13]	9	[12],[13]
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	53		33
Fixed income [Abstract]
Deferred compensation	(5)		(5)
Total assets	58		38
Total liabilities	(5)		(5)
Total net assets	53		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	[12]	5	[12]
Rabbi trust investments subtotal	5		5	[12]
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	53		33
Fixed income [Abstract]
Total assets	58		38
Total net assets	58		38
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	5	[12]	5	[12]
Rabbi trust investments subtotal	5		5	[12]
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 $13 million and $30 million at September 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 assets of $7 million at both September 30, 2013 and December 31, 2012. 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 $49 million related to deferred compensation at September 30, 2013, and $53 million related to deferred compensation and $16 million related to Supplemental Executive Retirement Plan at December 31, 2012. .

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

[6] Includes collateral postings (received) from counterparties. Collateral posted (received) from counterparties, net of collateral paid to counterparties, totaled $108 million, $58 million and $(20) million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of September 30, 2013. Collateral posted (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 $106 million at September 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 assets of $7 at both September 30, 2013 December 31, 2012. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.

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

[10] 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.

[11] 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.

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

[13]