Fair Value of Financial Assets and Liabilities - Fair Value Measurements of Assets and Liabilities, Recurring and Nonrecurring (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	$ 1,107		$ 1,119
Fixed income
Other investments	5		5
Total assets	14,236		14,081
Deferred compensation obligation	(103)		(107)
Total liabilities	(711)		(744)
Total net assets	13,525		13,337
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(103)		(107)
Mark-to-market derivative liabilities	491		403
Derivative Liability, Current	117		234
Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	264		245
Equity
Domestic	4,686		4,630
Foreign	639		612
Equity funds subtotal	5,325		5,242
Fixed income
U.S. Treasury and agencies	1,201		996
State and municipal debt	423		438
Financial Instruments, Owned, at Fair Value	488
Other	89		95
Corporate debt securities	2,159		2,262
Commingled funds			511
Fixed income subtotal	4,360		4,302
Middle market lending	363		366
Private Equity	95		83
Other	323		301
Fair Value Assets Measured On Recurring Basis Real Estate	9		3
Nuclear decommissioning trust fund investments subtotal	10,739		10,542
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	(27)		(5)
Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	19		15
Equity
Domestic	7		7
Fixed income
U.S. Treasury and agencies	5		8
State and municipal debt	10		10
Financial Instruments, Owned, at Fair Value	4
Corporate debt securities	84		89
Commingled funds			3
Fixed income subtotal	103		110
Middle market lending	178		184
Pledged assets for Zion Station decommissioning subtotal	307		316
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	1		3
Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents			1
Fixed income
Mutual funds			46
Rabbi trust investments in mutual funds(d)(e)	48		47
Deferred compensation obligation	(47)		(45)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(47)		(45)
Supplemental executive retirement plan fair value	1		1
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	36		35
Commodity Mark To Market Derivative Assets [Member]
Fixed income
Economic hedges	6,981		6,813
Proprietary trading	501		512
Effect of netting and allocation of collateral	5,488		5,296
Commodity derivative assets subtotal	1,994		2,029
Commodity Mark To Market Derivative Liabilities [Member]
Fixed income
Economic hedges	(6,762)		(6,694)
Proprietary trading	(514)		(532)
Effect of netting and allocation of collateral	(6,834)		(6,702)
Commodity derivative assets subtotal	(442)		(524)
Interest Rate Mark To Market Derivative Assets [Member]
Fixed income
Effect of netting and allocation of collateral	(44)		(48)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	(36)		(23)
Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income
Effect of netting and allocation of collateral	(52)		(54)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	(166)		(113)
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	1,107		1,119
Fixed income
Other investments	2		2
Total assets	5,485		5,305
Deferred compensation obligation	0		0
Total liabilities	43		(9)
Total net assets	5,528		5,296
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	425		434
Fair Value, Inputs, Level 1 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	224		208
Equity
Domestic	2,459		2,423
Foreign	639		612
Equity funds subtotal	3,098		3,035
Fixed income
U.S. Treasury and agencies	1,201		996
State and municipal debt	0		0
Financial Instruments, Owned, at Fair Value	0
Other	0		0
Corporate debt securities	0		0
Commingled funds			0
Fixed income subtotal	1,201		996
Middle market lending	0		0
Private Equity	0		0
Other	0		0
Fair Value Assets Measured On Recurring Basis Real Estate	0
Nuclear decommissioning trust fund investments subtotal	4,523		4,239
Fair Value, Inputs, Level 1 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Equity
Domestic	6		6
Fixed income
U.S. Treasury and agencies	2		5
State and municipal debt	0		0
Financial Instruments, Owned, at Fair Value	0
Corporate debt securities	0		0
Commingled funds			0
Fixed income subtotal	2		5
Middle market lending	0		0
Pledged assets for Zion Station decommissioning subtotal	8		11
Fair Value, Inputs, Level 1 [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents			1
Fixed income
Mutual funds			46
Rabbi trust investments in mutual funds(d)(e)	48		47
Fair Value, Inputs, Level 1 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income
Economic hedges	1,510		1,667
Proprietary trading	176		201
Effect of netting and allocation of collateral	1,899		1,982
Commodity derivative assets subtotal	(213)		(114)
Fair Value, Inputs, Level 1 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income
Economic hedges	(2,126)		(2,241)
Proprietary trading	(169)		(195)
Effect of netting and allocation of collateral	(2,324)		(2,416)
Commodity derivative assets subtotal	29		(20)
Fair Value, Inputs, Level 1 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income
Effect of netting and allocation of collateral	(8)		(17)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	(10)		(1)
Fair Value, Inputs, Level 1 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income
Effect of netting and allocation of collateral	(15)		(25)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	14		11
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income
Other investments	0		0
Total assets	6,639		6,747
Deferred compensation obligation	(103)		(107)
Total liabilities	(363)		(427)
Total net assets	6,276		6,320
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(103)		(107)
Collateral received from counterparties, net of collateral paid to counterparties	736		800
Fair Value, Inputs, Level 2 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	40		37
Equity
Domestic	2,227		2,207
Foreign	0		0
Equity funds subtotal	2,227		2,207
Fixed income
U.S. Treasury and agencies	0		0
State and municipal debt	423		438
Financial Instruments, Owned, at Fair Value	488
Other	89		95
Corporate debt securities	1,911		2,023
Commingled funds			511
Fixed income subtotal	2,911		3,067
Middle market lending	0		0
Private Equity	0		0
Other	323		301
Fair Value Assets Measured On Recurring Basis Real Estate	0
Nuclear decommissioning trust fund investments subtotal	5,501		5,612
Fair Value, Inputs, Level 2 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	19		15
Equity
Domestic	1		1
Fixed income
U.S. Treasury and agencies	3		3
State and municipal debt	10		10
Financial Instruments, Owned, at Fair Value	4
Corporate debt securities	84		89
Commingled funds			3
Fixed income subtotal	101		105
Middle market lending	0		0
Pledged assets for Zion Station decommissioning subtotal	121		121
Fair Value, Inputs, Level 2 [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents			0
Fixed income
Mutual funds			0
Rabbi trust investments in mutual funds(d)(e)	0		0
Fair Value, Inputs, Level 2 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income
Economic hedges	3,554		3,465
Proprietary trading	286		284
Effect of netting and allocation of collateral	2,849		2,757
Commodity derivative assets subtotal	991		992
Fair Value, Inputs, Level 2 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income
Economic hedges	(3,370)		(3,458)
Proprietary trading	(295)		(295)
Effect of netting and allocation of collateral	(3,585)		(3,557)
Commodity derivative assets subtotal	(80)		(196)
Fair Value, Inputs, Level 2 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income
Effect of netting and allocation of collateral	(36)		(31)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	(26)		(22)
Fair Value, Inputs, Level 2 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income
Effect of netting and allocation of collateral	(37)		(29)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	(180)		(124)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income
Other investments	3		3
Total assets	2,112		2,029
Deferred compensation obligation	0		0
Total liabilities	(391)		(308)
Total net assets	1,721		1,721
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	185		172
Fair Value, Inputs, Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Equity
Domestic	0		0
Foreign	0		0
Equity funds subtotal	0		0
Fixed income
U.S. Treasury and agencies	0		0
State and municipal debt	0		0
Financial Instruments, Owned, at Fair Value	0
Other	0		0
Corporate debt securities	248		239
Commingled funds			0
Fixed income subtotal	248		239
Middle market lending	363		366
Private Equity	95		83
Other	0		0
Fair Value Assets Measured On Recurring Basis Real Estate	9		3
Nuclear decommissioning trust fund investments subtotal	715		691
Fair Value, Inputs, Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Equity
Domestic	0		0
Fixed income
U.S. Treasury and agencies	0		0
State and municipal debt	0		0
Financial Instruments, Owned, at Fair Value	0
Corporate debt securities	0		0
Commingled funds			0
Fixed income subtotal	0		0
Middle market lending	178		184
Pledged assets for Zion Station decommissioning subtotal	178		184
Fair Value, Inputs, Level 3 [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents			0
Fixed income
Mutual funds			0
Rabbi trust investments in mutual funds(d)(e)	0		0
Fair Value, Inputs, Level 3 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income
Economic hedges	1,917		1,681
Proprietary trading	39		27
Effect of netting and allocation of collateral	740		557
Commodity derivative assets subtotal	1,216		1,151
Fair Value, Inputs, Level 3 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income
Economic hedges	(1,266)		(995)
Proprietary trading	(50)		(42)
Effect of netting and allocation of collateral	(925)		(729)
Commodity derivative assets subtotal	(391)		(308)
Fair Value, Inputs, Level 3 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income
Effect of netting and allocation of collateral	0		0
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	0		0
Fair Value, Inputs, Level 3 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income
Effect of netting and allocation of collateral	0		0
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	0		0
Designated as Hedging Instrument [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	32		31
Designated as Hedging Instrument [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		0
Designated as Hedging Instrument [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	32		31
Designated as Hedging Instrument [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		0
Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral			(41)
Derivative Liability, Fair Value, Amount Offset Against Collateral	(17)
Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0		0
Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(17)		(41)
Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0		0
Derivative [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	29		13
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Mark-to-market derivative liabilities	332		289
Derivative Liability, Current	110		235
Derivative [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		0
Derivative [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	29		13
Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		0
Derivative [Member] | Derivative Financial Instruments, Liabilities [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral			(103)
Derivative Liability, Fair Value, Amount Offset Against Collateral	(186)
Derivative [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0		0
Derivative [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(186)		(103)
Derivative [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0		0
Interest Rate Swap [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	19		27
Interest Rate Swap [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	18		18
Interest Rate Swap [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	1		9
Interest Rate Swap [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		0
Interest Rate Swap [Member] | Derivative Financial Instruments, Liabilities [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral			(23)
Derivative Liability, Fair Value, Amount Offset Against Collateral	(15)
Interest Rate Swap [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(1)		(14)
Interest Rate Swap [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(14)		(9)
Interest Rate Swap [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0		0
Exelon Generation Co L L C [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	220		405
Fixed income
Derivative Liability, Fair Value, Amount Offset Against Collateral	1,138		1,140
Other investments	3		3
Total assets	13,312		13,329
Deferred compensation obligation	(30)		(31)
Total liabilities	(248)		(350)
Total net assets	13,064		12,979
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(30)		(31)
Mark-to-market derivative liabilities	121		105
Derivative Liability, Current	97		214
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	264		245
Equity
Domestic	4,686		4,630
Foreign	639		612
Equity funds subtotal	5,325		5,242
Fixed income
U.S. Treasury and agencies	1,201		996
State and municipal debt	423		438
Financial Instruments, Owned, at Fair Value	488
Other	89		95
Corporate debt securities	2,159		2,262
Commingled funds			511
Fixed income subtotal	4,360		4,302
Middle market lending	363		366
Private Equity	95		83
Other	323		301
Fair Value Assets Measured On Recurring Basis Real Estate	9		3
Nuclear decommissioning trust fund investments subtotal	10,739		10,542
Exelon Generation Co L L C [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	19		15
Equity
Domestic	7		7
Fixed income
U.S. Treasury and agencies	5		8
State and municipal debt	10		10
Financial Instruments, Owned, at Fair Value	4
Corporate debt securities	84		89
Commingled funds			3
Fixed income subtotal	103		110
Middle market lending	178		184
Pledged assets for Zion Station decommissioning subtotal	307		316
Exelon Generation Co L L C [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents			0
Fixed income
Mutual funds			16
Rabbi trust investments in mutual funds(d)(e)	16		16
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	12		11
Exelon Generation Co L L C [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income
Economic hedges	6,981		6,813
Proprietary trading	501		512
Effect of netting and allocation of collateral	5,488		5,296
Commodity derivative assets subtotal	1,994		2,029
Exelon Generation Co L L C [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income
Economic hedges	(6,521)		(6,487)
Proprietary trading	(514)		(532)
Effect of netting and allocation of collateral	(6,834)		(6,702)
Commodity derivative assets subtotal	(201)		(317)
Exelon Generation Co L L C [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income
Effect of netting and allocation of collateral	(13)		(29)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	(33)		(18)
Exelon Generation Co L L C [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income
Effect of netting and allocation of collateral	(21)		(35)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	(17)		(2)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	220		405
Fixed income
Other investments	0		0
Total assets	4,564		4,558
Deferred compensation obligation	0		0
Total liabilities	43		(9)
Total net assets	4,607		4,549
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	224		208
Equity
Domestic	2,459		2,423
Foreign	639		612
Equity funds subtotal	3,098		3,035
Fixed income
U.S. Treasury and agencies	1,201		996
State and municipal debt	0		0
Financial Instruments, Owned, at Fair Value	0
Other	0		0
Corporate debt securities	0		0
Commingled funds			0
Fixed income subtotal	1,201		996
Middle market lending	0		0
Private Equity	0		0
Other	0		0
Fair Value Assets Measured On Recurring Basis Real Estate	0
Nuclear decommissioning trust fund investments subtotal	4,523		4,239
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Equity
Domestic	6		6
Fixed income
U.S. Treasury and agencies	2		5
State and municipal debt	0		0
Financial Instruments, Owned, at Fair Value	0
Corporate debt securities	0		0
Commingled funds			0
Fixed income subtotal	2		5
Middle market lending	0		0
Pledged assets for Zion Station decommissioning subtotal	8		11
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents			0
Fixed income
Mutual funds			16
Rabbi trust investments in mutual funds(d)(e)	16		16
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income
Economic hedges	1,510		1,667
Proprietary trading	176		201
Effect of netting and allocation of collateral	1,899		1,982
Commodity derivative assets subtotal	(213)		(114)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income
Economic hedges	(2,126)		(2,241)
Proprietary trading	(169)		(195)
Effect of netting and allocation of collateral	(2,324)		(2,416)
Commodity derivative assets subtotal	29		(20)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income
Effect of netting and allocation of collateral	(8)		(17)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	(10)		(1)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income
Effect of netting and allocation of collateral	(15)		(25)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	14		11
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income
Other investments	0		0
Total assets	6,636		6,742
Deferred compensation obligation	(30)		(31)
Total liabilities	(141)		(240)
Total net assets	6,495		6,502
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(30)		(31)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	40		37
Equity
Domestic	2,227		2,207
Foreign	0		0
Equity funds subtotal	2,227		2,207
Fixed income
U.S. Treasury and agencies	0		0
State and municipal debt	423		438
Financial Instruments, Owned, at Fair Value	488
Other	89		95
Corporate debt securities	1,911		2,023
Commingled funds			511
Fixed income subtotal	2,911		3,067
Middle market lending	0		0
Private Equity	0		0
Other	323		301
Fair Value Assets Measured On Recurring Basis Real Estate	0		0
Nuclear decommissioning trust fund investments subtotal	5,501		5,612
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	19		15
Equity
Domestic	1		1
Fixed income
U.S. Treasury and agencies	3		3
State and municipal debt	10		10
Financial Instruments, Owned, at Fair Value	4
Corporate debt securities	84		89
Commingled funds			3
Fixed income subtotal	101		105
Middle market lending	0		0
Pledged assets for Zion Station decommissioning subtotal	121		121
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents			0
Fixed income
Mutual funds			0
Rabbi trust investments in mutual funds(d)(e)	0		0
Commodity derivative assets subtotal			992
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income
Economic hedges	3,554		3,465
Proprietary trading	286		284
Effect of netting and allocation of collateral	2,849		2,757
Commodity derivative assets subtotal	991
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income
Economic hedges	(3,370)		(3,458)
Proprietary trading	(295)		(295)
Effect of netting and allocation of collateral	(3,585)		(3,557)
Commodity derivative assets subtotal	(80)		(196)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income
Effect of netting and allocation of collateral	(5)		(12)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	(23)		(17)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income
Effect of netting and allocation of collateral	(6)		(10)
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	(31)		(13)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income
Other investments	3		3
Total assets	2,112		2,029
Deferred compensation obligation	0		0
Total liabilities	(150)		(101)
Total net assets	1,962		1,928
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Equity
Domestic	0		0
Foreign	0		0
Equity funds subtotal	0		0
Fixed income
U.S. Treasury and agencies	0		0
State and municipal debt	0		0
Financial Instruments, Owned, at Fair Value	0
Other	0		0
Corporate debt securities	248		239
Commingled funds			0
Fixed income subtotal	248		239
Middle market lending	363		366
Private Equity	95		83
Other	0		0
Fair Value Assets Measured On Recurring Basis Real Estate	9		3
Nuclear decommissioning trust fund investments subtotal	715		691
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Equity
Domestic	0		0
Fixed income
U.S. Treasury and agencies	0		0
State and municipal debt	0		0
Financial Instruments, Owned, at Fair Value	0
Corporate debt securities	0		0
Commingled funds			0
Fixed income subtotal	0		0
Middle market lending	178		184
Pledged assets for Zion Station decommissioning subtotal	178		184
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Rabbi Trust Investments [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents			0
Fixed income
Mutual funds			0
Rabbi trust investments in mutual funds(d)(e)	0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income
Economic hedges	1,917		1,681
Proprietary trading	39		27
Effect of netting and allocation of collateral	740		557
Commodity derivative assets subtotal	1,216		1,151
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income
Economic hedges	(1,025)		(788)
Proprietary trading	(50)		(42)
Effect of netting and allocation of collateral	(925)		(729)
Commodity derivative assets subtotal	(150)		(101)
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income
Effect of netting and allocation of collateral	0		0
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	0		0
Exelon Generation Co L L C [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income
Effect of netting and allocation of collateral	0		0
Interest rate and foreign currency derivative assets
Interest rate and foreign currency derivative assets subtotal	0		0
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		8
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		0
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		8
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		0
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	17		(12)
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0		0
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(17)		(12)
Exelon Generation Co L L C [Member] | Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0		0
Exelon Generation Co L L C [Member] | Derivative [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	27		12
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Mark-to-market derivative liabilities	111	[1]	102	[2]
Derivative Liability, Current	90	[1]	215	[2]
Exelon Generation Co L L C [Member] | Derivative [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		0
Exelon Generation Co L L C [Member] | Derivative [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	27		12
Exelon Generation Co L L C [Member] | Derivative [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		0
Exelon Generation Co L L C [Member] | Derivative [Member] | Derivative Financial Instruments, Liabilities [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral			(2)
Derivative Liability, Fair Value, Amount Offset Against Collateral	(6)
Exelon Generation Co L L C [Member] | Derivative [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0		0
Exelon Generation Co L L C [Member] | Derivative [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(6)		(2)
Exelon Generation Co L L C [Member] | Derivative [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0		0
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	19		27
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative Liability, Current	3
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	18		18
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	1		9
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0		0
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Derivative Financial Instruments, Liabilities [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral			(23)
Derivative Liability, Fair Value, Amount Offset Against Collateral	(15)
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 1 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(1)		(14)
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 2 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(14)		(9)
Exelon Generation Co L L C [Member] | Interest Rate Swap [Member] | Derivative Financial Instruments, Liabilities [Member] | Fair Value, Inputs, Level 3 [Member]
Fixed income
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0		0
PECO Energy Co [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	5		12
Fixed income
Mutual funds			9
Commodity derivative assets subtotal	0		0
Total assets	14		21
Deferred compensation obligation	(14)		(15)
Total liabilities	(14)		(15)
Total net assets	0		6
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(14)		(15)
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, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	5		12
Fixed income
Mutual funds			9
Commodity derivative assets subtotal	0		0
Total assets	14		21
Deferred compensation obligation	0		0
Total liabilities	0		0
Total net assets	14		21
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income
Commodity derivative assets subtotal	0		0
Total assets	0		0
Deferred compensation obligation	(14)		(15)
Total liabilities	(14)		(15)
Total net assets	(14)		(15)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(14)		(15)
PECO Energy Co [Member] | Fair Value, Inputs, Level 2 [Member] | Rabbi Trust Investments [Member]
Fixed income
Mutual funds	0		0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income
Commodity derivative assets subtotal	0		0
Total assets	0		0
Deferred compensation obligation	0		0
Total liabilities	0		0
Total net assets	0		0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
PECO Energy Co [Member] | Fair Value, Inputs, Level 3 [Member] | Rabbi Trust Investments [Member]
Fixed income
Mutual funds	0		0
Commonwealth Edison Co [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	67		25
Fixed income
Commodity derivative assets subtotal	241		207
Total assets	67		25
Deferred compensation obligation	(8)		(8)
Total liabilities	(249)		(215)
Total net assets	(182)		(190)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(8)		(8)
Mark-to-market derivative liabilities	221		187
Derivative Liability, Current	20		20
Commonwealth Edison Co [Member] | Rabbi Trust Investments [Member]
Fixed income
Mutual funds	0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	67		25
Fixed income
Commodity derivative assets subtotal	0		0
Total assets	67		25
Deferred compensation obligation	0		0
Total liabilities	0		0
Total net assets	67		25
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income
Mutual funds	0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income
Commodity derivative assets subtotal	0		0
Total assets	0		0
Deferred compensation obligation	(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 2 [Member] | Rabbi Trust Investments [Member]
Fixed income
Mutual funds	0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income
Commodity derivative assets subtotal	241		207
Total assets	0		0
Deferred compensation obligation	0		0
Total liabilities	(241)		(207)
Total net assets	(241)		(207)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Commonwealth Edison Co [Member] | Fair Value, Inputs, Level 3 [Member] | Rabbi Trust Investments [Member]
Fixed income
Mutual funds	0		0
Baltimore Gas and Electric Company [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	75		103
Fixed income
Mutual funds			5
Commodity derivative assets subtotal	0		0
Total assets	80		108
Deferred compensation obligation	(4)		(5)
Total liabilities	(4)		(5)
Total net assets	76		103
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(4)		(5)
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	75		103
Fixed income
Mutual funds	5		5
Commodity derivative assets subtotal	0		0
Total assets	80		108
Deferred compensation obligation	0		0
Total liabilities	0		0
Total net assets	80		108
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income
Commodity derivative assets subtotal	0		0
Total assets	0		0
Deferred compensation obligation	(4)		(5)
Total liabilities	(4)		(5)
Total net assets	(4)		(5)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(4)		(5)
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 2 [Member] | Rabbi Trust Investments [Member]
Fixed income
Mutual funds	0		0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets, Liabilities and Stockholders' Equity Measured on Recurring Basis [Abstract]
Cash equivalents	0		0
Fixed income
Commodity derivative assets subtotal	0		0
Total assets	0		0
Deferred compensation obligation	0		0
Total liabilities	0		0
Total net assets	0		0
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0		0
Baltimore Gas and Electric Company [Member] | Fair Value, Inputs, Level 3 [Member] | Rabbi Trust Investments [Member]
Fixed income
Mutual funds	$ 0		$ 0

[1] Current and noncurrent assets are shown net of collateral of $387 million and $192 million, respectively, and current and noncurrent liabilities are shown net of collateral of $519 million and $248 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $1,346 million at March 31, 2015.

[2] Current and noncurrent assets are shown net of collateral of $416 million and $171 million, respectively, and current and noncurrent liabilities are shown net of collateral of $599 million and $220 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $1,406 million at December 31, 2014.