Fair Value of Financial Assets and Liabilities (Fair Value Measurements, Recurring and Nonrecurring) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	$ 518	[1]	$ 1,230	[1]
Fixed income [Abstract]
Other investments	23		15
Deferred compensation	(107)		(114)
Total assets	10,525		11,162
Total liabilities	(645)		(573)
Total net assets	9,880		10,589
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	107		114
Mark-to-market derivative liabilities (current liabilities)	251		159
Mark-to-market derivative liabilities (noncurrent liabilities)	287		300
Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	304		459
Equity Securities [Abstract]
Equity securities	1,813		1,776
Exchange traded funds	113		115
Commingled funds	2,053		2,271
Equity securities subtotal	3,979
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	903		882
Debt securities issued by states of the United States and political subdivisions of the states	295		294
Debt securities issued by foreign governments	87		87
Corporate debt securities	1,921		1,784
Federal agency mortgage-backed securities	9		10
Commercial mortgage-backed securities (non-agency)	40		40
Residential mortgage-backed securities (non-agency)	7		7
Mutual funds fixed income	278		18
Fixed income subtotal	3,540		3,122
Private equity	4		5
Direct lending securities	356		314
Other debt obligations	15		14
Nuclear decommissioning trust fund investments subtotal	8,198	[2]	8,076	[2]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	17		(5)
Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	35		26
Equity Securities [Abstract]
Equity securities	5		16
Equity securities subtotal	5		16
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	40		49
Debt securities issued by states of the United States and political subdivisions of the states	18		20
Corporate debt securities	180		227
Fixed income subtotal	238		296
Direct lending securities	137		112
Other debt obligations			1
Pledged assets for Zion Station decommissioning subtotal	415	[3]	451	[3]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from pledged assets	14		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	42	[4],[5]	54	[4],[5]
Rabbi trust investments subtotal	44		56
Deferred compensation	(41)		(53)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	41		53
Supplemental executive retirement plan fair value	1		1
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	33		32
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	13		17
Fair value of energy swap contract noncurrent liability	155		176
Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	4,641		3,960
Proprietary trading	1,341		1,761
Effect of netting and allocation of collateral received/(paid)	(4,694)	[6]	(4,424)	[6]
Mark-to-market subtotal	1,288		1,297
Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(4,463)		(3,020)
Proprietary trading	(1,318)		(1,703)
Effect of netting and allocation of collateral received/(paid)	5,261	[6]	4,280	[6]
Mark-to-market subtotal	(520)		(443)
Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(22)		32
Interest rate mark to market	61		69
Interest rate mark-to-market Subtotal	39		37
Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(28)		32
Interest rate mark to market	(46)		48
Interest rate mark-to-market Subtotal	(18)		16
Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	518	[1]	1,230	[1]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)			(31)
Other investments	13		0
Deferred compensation	0		0
Total assets	3,874		4,533
Total liabilities	0		1
Total net assets	3,874		4,534
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	117		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	304		459
Equity Securities [Abstract]
Equity securities	1,813		1,776
Exchange traded funds	113		115
Commingled funds	0
Equity securities subtotal	1,926		1,891
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	903		882
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	903		882
Direct lending securities	0
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	3,133	[2]	3,232	[2]
Fair Value Inputs Level 1 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	4		16
Equity securities subtotal	4		16
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	36		45
Debt securities issued by states of the United States and political subdivisions of the states	0
Corporate debt securities	0
Fixed income subtotal	36		45
Direct lending securities	0
Pledged assets for Zion Station decommissioning subtotal	40	[3]	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	42	[4],[5]	54	[4],[5]
Rabbi trust investments subtotal	44		56
Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	592		493
Proprietary trading	354		324
Effect of netting and allocation of collateral received/(paid)	(826)	[6]	(863)	[6]
Mark-to-market subtotal	120		(46)
Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(586)		(540)
Proprietary trading	(357)		(328)
Effect of netting and allocation of collateral received/(paid)	943	[6]	869	[6]
Mark-to-market subtotal	0		1
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)	(18)		(30)
Interest rate mark to market	24		30
Interest rate mark-to-market Subtotal	6		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)	25
Interest rate mark to market	(25)				31
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	(107)		(114)
Total assets	5,479		5,575
Total liabilities	(225)		(269)
Total net assets	5,254		5,306
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	107		114
Collateral received from counterparties, net of collateral paid to counterparties	332		(124)
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	2,053		2,271
Equity securities subtotal	2,053		2,271
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		294
Debt securities issued by foreign governments	87		87
Corporate debt securities	1,795		1,753
Federal agency mortgage-backed securities	9		10
Commercial mortgage-backed securities (non-agency)	40		40
Residential mortgage-backed securities (non-agency)	7		7
Mutual funds fixed income	278		18
Fixed income subtotal	2,511		2,209
Direct lending securities	0
Other debt obligations	15		14
Nuclear decommissioning trust fund investments subtotal	4,579	[2]	4,494	[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	35		26
Equity Securities [Abstract]
Equity securities	1
Equity securities subtotal	1		0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	4		4
Debt securities issued by states of the United States and political subdivisions of the states	18		20
Corporate debt securities	180		227
Fixed income subtotal	202		251
Direct lending securities	0
Other debt obligations			1
Pledged assets for Zion Station decommissioning subtotal	238	[3]	278	[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	2,778		2,582
Proprietary trading	808		1,315
Effect of netting and allocation of collateral received/(paid)	(2,957)	[6]	(3,131)	[6]
Mark-to-market subtotal	629		766
Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(2,624)		(1,890)
Proprietary trading	(765)		(1,256)
Effect of netting and allocation of collateral received/(paid)	3,289	[6]	3,007	[6]
Mark-to-market subtotal	(100)		(139)
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)	(4)		2
Interest rate mark to market	37		39
Interest rate mark-to-market Subtotal	33		37
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)	(3)		(1)
Interest rate mark to market	(21)		17
Interest rate mark-to-market Subtotal	(18)		16
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]
Other investments	10		15
Deferred compensation	0		0
Total assets	1,172		1,054
Total liabilities	(420)		(305)
Total net assets	752		749
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	118		(26)
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	126		31
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	126		31
Private equity	4		5
Direct lending securities	356		314
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	486	[2]	350	[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
Fixed income subtotal	0		0
Direct lending securities	137		112
Pledged assets for Zion Station decommissioning subtotal	137	[3]	112	[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	1,271		885
Proprietary trading	179		122
Effect of netting and allocation of collateral received/(paid)	(911)	[6]	(430)	[6]
Mark-to-market subtotal	539		577
Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(1,253)		(590)
Proprietary trading	(196)		(119)
Effect of netting and allocation of collateral received/(paid)	1,029	[6]	404	[6]
Mark-to-market subtotal	(420)		(305)
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	329		1,006	[1]
Fixed income [Abstract]
Other investments	23		15
Deferred compensation	(29)		(29)
Total assets	10,296		10,888
Total liabilities	(398)		(291)
Total net assets	9,898		10,597
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	29		29
Mark-to-market derivative liabilities (current liabilities)	238		142
Mark-to-market derivative liabilities (noncurrent liabilities)	131		120
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	304		459
Equity Securities [Abstract]
Equity securities	1,813		1,776
Exchange traded funds	113		115
Commingled funds	2,053		2,271
Equity securities subtotal	3,979		4,162
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	903		882
Debt securities issued by states of the United States and political subdivisions of the states	295		294
Debt securities issued by foreign governments	87		87
Corporate debt securities	1,921		1,784
Federal agency mortgage-backed securities	9		10
Commercial mortgage-backed securities (non-agency)	40		40
Residential mortgage-backed securities (non-agency)	7		7
Mutual funds fixed income	278		18
Fixed income subtotal	3,540		3,122
Private equity	4		5
Direct lending securities	356		314
Other debt obligations	15		14
Nuclear decommissioning trust fund investments subtotal	8,198	[2]	8,076	[2]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	17		(5)
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	35		26
Equity Securities [Abstract]
Equity securities	5		16
Equity securities subtotal	5		16
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	40		49
Debt securities issued by states of the United States and political subdivisions of the states	18		20
Corporate debt securities	180		227
Fixed income subtotal	238		296
Direct lending securities	137		112
Other debt obligations			1
Pledged assets for Zion Station decommissioning subtotal	415	[3]	451	[3]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	14		7
Exelon Generation Co L L C [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	1		0
Fixed income [Abstract]
Mutual funds	13	[7]	13	[7]
Rabbi trust investments subtotal	14		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	10		10
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		0
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	4,641		3,960
Proprietary trading	1,341		1,761
Effect of netting and allocation of collateral received/(paid)	(4,694)	[6]	(4,424)	[6]
Mark-to-market subtotal	1,288		1,297
Exelon Generation Co L L C [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges	0
Other derivatives	(4,295)		(2,827)
Proprietary trading	(1,318)		(1,703)
Effect of netting and allocation of collateral received/(paid)	5,261	[6]	4,280	[6]
Mark-to-market subtotal	(352)		(250)
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)	22		32
Interest rate mark to market	51		62
Interest rate mark-to-market Subtotal	29		30
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)	(28)		(32)
Interest rate mark to market	(45)		(44)
Interest rate mark-to-market Subtotal	(17)		(12)
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	329		1,006	[1]
Fixed income [Abstract]
Other investments	13		0
Deferred compensation	0
Total assets	3,655		4,266
Total liabilities	0		1
Total net assets	3,655		4,267
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	117				6
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	304		459
Equity Securities [Abstract]
Equity securities	1,813		1,776
Exchange traded funds	113		115
Commingled funds	0
Equity securities subtotal	1,926				1,891
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	903		882
Debt securities issued by states of the United States and political subdivisions of the states	0
Fixed income subtotal	903		882
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	3,133	[2]	3,232	[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		16
Equity securities subtotal	4		16
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	36		45
Fixed income subtotal	36		45
Pledged assets for Zion Station decommissioning subtotal	40	[3]	61	[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	1		0
Fixed income [Abstract]
Mutual funds	13	[7]	13	[7]
Rabbi trust investments subtotal	14		13
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	592		493
Proprietary trading	354		324
Effect of netting and allocation of collateral received/(paid)	(826)	[6]	(863)	[6]
Mark-to-market subtotal	120		(46)
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	(586)		(540)
Proprietary trading	(357)		(328)
Effect of netting and allocation of collateral received/(paid)	943	[6]	869	[6]
Mark-to-market subtotal	0		1
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)	18		30
Interest rate mark to market	24		30
Interest rate mark-to-market Subtotal	6
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)	(25)		(31)
Interest rate mark to market	(25)		(31)
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	(29)		(29)
Total assets	5,469		5,568
Total liabilities	(146)		(180)
Total net assets	5,323		5,388
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	29		29
Collateral received from counterparties, net of collateral paid to counterparties	332				(124)
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	2,053		2,271
Equity securities subtotal	2,053		2,271
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		294
Debt securities issued by foreign governments	87		87
Corporate debt securities	1,795		1,753
Federal agency mortgage-backed securities	9		10
Commercial mortgage-backed securities (non-agency)	40		40
Residential mortgage-backed securities (non-agency)	7		7
Mutual funds fixed income	278		18
Fixed income subtotal	2,511		2,209
Other debt obligations	15		14
Nuclear decommissioning trust fund investments subtotal	4,579	[2]	4,494	[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	35		26
Equity Securities [Abstract]
Equity securities	1
Equity securities subtotal	1		0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	4		4
Debt securities issued by states of the United States and political subdivisions of the states	18		20
Corporate debt securities	180		227
Fixed income subtotal	202		251
Direct lending securities	0
Other debt obligations			1
Pledged assets for Zion Station decommissioning subtotal	238	[3]	278	[3]
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	2,778		2,582
Proprietary trading	808		1,315
Effect of netting and allocation of collateral received/(paid)	(2,957)	[6]	(3,131)	[6]
Mark-to-market subtotal	629		766
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	(2,624)		(1,890)
Proprietary trading	(765)		(1,256)
Effect of netting and allocation of collateral received/(paid)	3,289	[6]	3,007	[6]
Mark-to-market subtotal	(100)		(139)
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)	4		2
Interest rate mark to market	27		32
Interest rate mark-to-market Subtotal	23		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)	(3)		(1)
Interest rate mark to market	(20)		(13)
Interest rate mark-to-market Subtotal	(17)		(12)
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	10		15
Deferred compensation	0
Total assets	1,172		1,054
Total liabilities	(252)		(112)
Total net assets	920		942
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	118				(26)
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
Corporate debt securities	126		31
Mutual funds fixed income	0
Fixed income subtotal	126		31
Private equity	4		5
Direct lending securities	356		314
Other debt obligations	0
Nuclear decommissioning trust fund investments subtotal	486	[2]	350	[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	137		112
Pledged assets for Zion Station decommissioning subtotal	137	[3]	112	[3]
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	1,271		885
Proprietary trading	179		122
Effect of netting and allocation of collateral received/(paid)	(911)	[6]	(430)	[6]
Mark-to-market subtotal	539		577
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	(1,085)		(397)
Proprietary trading	(196)		(119)
Effect of netting and allocation of collateral received/(paid)	1,029	[6]	404	[6]
Mark-to-market subtotal	(252)		(112)
Commonwealth Edison Co [Member]
Fixed income [Abstract]
Deferred compensation	(8)		(8)
Total assets	2		5
Total liabilities	(176)		(201)
Total net assets	(174)		(196)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	8		8
Mark-to-market derivative liabilities (current liabilities)	13		17
Mark-to-market derivative liabilities (noncurrent liabilities)	155		176
Commonwealth Edison Co [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	2		5
Rabbi trust investments subtotal	2		5
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		0
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	13		17
Fair value of energy swap contract noncurrent liability	155		176
Commonwealth Edison Co [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	168	[8]	193	[8]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member]
Fixed income [Abstract]
Deferred compensation	0
Total assets	2		5
Total liabilities	0		0
Total net assets	2		5
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	2		5
Rabbi trust investments subtotal	2		5
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	0	[8]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member]
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	[8]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member]
Fixed income [Abstract]
Deferred compensation	0
Total assets	0		0
Total liabilities	(168)		(193)
Total net assets	(168)		(193)
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	168	[8]	193	[8]
PECO Energy Co [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	32		175
Fixed income [Abstract]
Deferred compensation	(17)		(17)
Total assets	41		184
Total liabilities	(17)		(17)
Total net assets	24		167
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	17		17
PECO Energy Co [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	9		9
Rabbi trust investments subtotal	9	[10],[9]	9	[10],[9]
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		14
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	32		175
Fixed income [Abstract]
Total assets	41		184
Total net assets	41		184
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	[10],[9]	9	[10],[9]
PECO Energy Co [Member] | Fair Value Inputs Level 2 [Member]
Fixed income [Abstract]
Deferred compensation	(17)		(17)
Total liabilities	(17)		(17)
Total net assets	(17)		(17)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	17		17
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] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	4	[9]	6	[9]
Baltimore Gas and Electric Company [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	30		31
Fixed income [Abstract]
Total assets	34		37
Total net assets	30		31
Baltimore Gas and Electric Company [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	(4)		(6)
Total liabilities	(4)		(6)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	4		6
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	4	[9]	6	[9]
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	30		31
Fixed income [Abstract]
Total assets	34		37
Total net assets	34		37
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Total net assets	(4)		(6)
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	(4)		(6)
Total liabilities	(4)		(6)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	$ 4		$ 6

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

[2] Excludes net assets (liabilities) of $17 million and $(5) million at March 31, 2014 and December 31, 2013, 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 $14 million and $7 million at March 31, 2014 and December 31, 2013, 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 $41 million related to deferred compensation and $1 million related to Supplemental Executive Retirement Plan at March 31, 2014, and $53 million related to deferred compensation and $1 million related to Supplemental Executive Retirement Plan at December 31, 2013.

[5] Excludes $33 million and $32 million of the cash surrender value of life insurance investments at March 31, 2014 and December 31, 2013, respectively.

[6] Includes collateral postings (received) from counterparties. Collateral posted (received) from counterparties, net of collateral paid to counterparties, totaled $117 million, $332 million and $118 million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of March 31, 2014. Collateral posted (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.

[7] Excludes $10 million of the cash surrender value of life insurance investments at both March 31, 2014 and December 31, 2013.

[8] The Level 3 balance includes the current and noncurrent liability of $13 million and $155 million at March 31, 2014, respectively, and $17 million and $176 million at December 31, 2013, respectively, related to floating-to-fixed energy swap contracts with unaffiliated suppliers.

[9] Excludes $14 million of the cash surrender value of life insurance investments at both March 31, 2014 and December 31, 2013.

[10]