Fair Value of Financial Assets and Liabilities (Fair Value Measurements, Recurring and Nonrecurring) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	$ 995.00	[1]	$ 861.00	[1]
Fixed income [Abstract]
Debt securities issued by foreign governments			16.00
Deferred compensation	(102.00)		(73.00)
Total assets	10,785.00		9,268.00
Total liabilities	(735.00)		(311.00)
Total net assets	10,050.00		8,957.00
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	102.00		73.00
Mark-to-market derivative liabilities (current liabilities)	352.00		112.00
Mark-to-market derivative liabilities (noncurrent liabilities)	281.00		126.00
Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	245.00		562.00
Equity Securities [Abstract]
Equity securities	1,480.00		1,275.00
Commingled funds	1,933.00		1,822.00
Equity securities subtotal	3,413.00		3,097.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,057.00		1,047.00
Debt securities issued by states of the United States and political subdivisions of the states	321.00		541.00
Debt securities issued by foreign governments	93.00		16.00
Corporate debt securities	1,788.00		778.00
Federal agency mortgage-backed securities	24.00		357.00
Commercial mortgage-backed securities (non-agency)	45.00		83.00
Residential mortgage-backed securities (non-agency)	11.00		5.00
Mutual funds fixed income	23.00		47.00
Fixed income subtotal	3,362.00		2,874.00
Direct lending securities	183.00
Other debt obligations	15.00		18.00
Nuclear decommissioning trust fund investments subtotal	7,218.00	[2]	6,564.00	[2]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	30.00		(57.00)
Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	23.00
Equity Securities [Abstract]
Equity securities	14.00		35.00
Commingled funds	9.00		30.00
Equity securities subtotal	23.00		65.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	130.00		80.00
Debt securities issued by states of the United States and political subdivisions of the states	37.00		65.00
Corporate debt securities	249.00		314.00
Federal agency mortgage-backed securities	49.00		121.00
Commercial mortgage-backed securities (non-agency)	6.00		10.00
Residential mortgage-backed securities (non-agency)	89.00
Commingled funds fixed income			20.00
Fixed income subtotal	471.00		610.00
Direct lending securities			37.00
Other debt obligations	1.00		13.00
Pledged assets for Zion Station decommissioning subtotal	607.00	[3]	725.00	[3]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from pledged assets	7.00		9.00
Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	2.00		2.00
Fixed income [Abstract]
Mutual funds	69.00		34.00	[4],[5]
Rabbi trust investments subtotal	71.00		36.00
Deferred compensation	(53.00)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	53.00
Supplemental executive retirement plan fair value	16.00
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	28.00		25.00
Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Other investments	19.00
Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Cash flow hedges			857.00
Other derivatives	4,675.00		1,777.00
Proprietary trading	3,193.00		288.00
Effect of netting and allocation of collateral received/(paid)	(6,056.00)	[5]	(1,855.00)	[6]
Mark-to-market subtotal	1,812.00		1,067.00	[5]
Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges			(13.00)
Other derivatives	(3,566.00)		(1,257.00)
Proprietary trading	(3,121.00)		(264.00)
Effect of netting and allocation of collateral received/(paid)	6,087.00	[5]	1,315.00	[5]
Mark-to-market subtotal	(600.00)		(219.00)	[6]
Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	51.00
Interest rate mark to market	114.00		15.00
Interest rate marrk-to-market Subtotal	63.00
Interest Rate Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	(51.00)
Interest rate mark to market	(84.00)		(19.00)
Interest rate marrk-to-market Subtotal	(33.00)
Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	995.00	[1]	861.00	[1]
Fixed income [Abstract]
Total assets			3,837.00
Total liabilities	(83.00)		(1.00)
Total net assets	3,979.00		3,836.00
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties	219.00
Fair Value Inputs Level 1 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	245.00		562.00
Equity Securities [Abstract]
Equity securities	1,480.00		1,275.00
Equity securities subtotal	1,480.00		1,275.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,057.00		1,014.00
Fixed income subtotal	1,057.00		1,014.00
Nuclear decommissioning trust fund investments subtotal	2,782.00	[2]	2,851.00	[2]
Fair Value Inputs Level 1 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	14.00		35.00
Equity securities subtotal	14.00		35.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	118.00		54.00
Fixed income subtotal	118.00		54.00
Pledged assets for Zion Station decommissioning subtotal	132.00	[3]	89.00	[3]
Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	2.00		2.00
Fixed income [Abstract]
Mutual funds	69.00		34.00	[4],[5]
Rabbi trust investments subtotal	71.00		36.00
Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Other investments	2.00
Total assets	4,062.00
Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	861.00
Proprietary trading	1,042.00
Effect of netting and allocation of collateral received/(paid)	(1,823.00)	[5]
Mark-to-market subtotal	80.00
Fair Value Inputs Level 1 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(1,041.00)		(1.00)
Proprietary trading	(1,084.00)
Effect of netting and allocation of collateral received/(paid)	2,042.00	[5]
Mark-to-market subtotal	(83.00)		(1.00)	[6]
Fair Value Inputs Level 2 [Member]
Fixed income [Abstract]
Deferred compensation	(102.00)		(73.00)
Total assets			5,237.00
Total liabilities	(363.00)		(183.00)
Total net assets	5,415.00		5,054.00
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	102.00		73.00
Collateral received from counterparties, net of collateral paid to counterparties	(155.00)		532.00
Fair Value Inputs Level 2 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Equity Securities [Abstract]
Commingled funds	1,933.00		1,822.00
Equity securities subtotal	1,933.00		1,822.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies			33.00
Debt securities issued by states of the United States and political subdivisions of the states	321.00		541.00
Debt securities issued by foreign governments	93.00
Corporate debt securities	1,788.00		778.00
Federal agency mortgage-backed securities	24.00		357.00
Commercial mortgage-backed securities (non-agency)	45.00		83.00
Residential mortgage-backed securities (non-agency)	11.00		5.00
Mutual funds fixed income	23.00		47.00
Fixed income subtotal	2,305.00		1,860.00
Other debt obligations	15.00		18.00
Nuclear decommissioning trust fund investments subtotal	4,253.00	[2]	3,700.00	[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	23.00
Equity Securities [Abstract]
Commingled funds	9.00		30.00
Equity securities subtotal	9.00		30.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	12.00		26.00
Debt securities issued by states of the United States and political subdivisions of the states	37.00		65.00
Corporate debt securities	249.00		314.00
Federal agency mortgage-backed securities	49.00		121.00
Commercial mortgage-backed securities (non-agency)	6.00		10.00
Commingled funds fixed income			20.00
Fixed income subtotal	353.00		556.00
Other debt obligations	1.00		13.00
Pledged assets for Zion Station decommissioning subtotal	386.00	[3]	599.00	[3]
Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Total assets	5,778.00
Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Cash flow hedges			857.00
Other derivatives	3,173.00		1,653.00
Proprietary trading	2,078.00		240.00
Effect of netting and allocation of collateral received/(paid)	(4,175.00)	[5]	(1,827.00)	[6]
Mark-to-market subtotal	1,076.00		923.00	[5]
Fair Value Inputs Level 2 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges			(13.00)
Other derivatives	(2,289.00)		(1,137.00)
Proprietary trading	(1,959.00)		(236.00)
Effect of netting and allocation of collateral received/(paid)	4,020.00	[5]	1,295.00	[5]
Mark-to-market subtotal	(228.00)		(91.00)	[6]
Fair Value Inputs Level 2 [Member] | Interest Rate Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Effect of netting and allocation of collateral received/(paid)	51.00
Interest rate mark to market	114.00		15.00
Interest rate marrk-to-market Subtotal	63.00
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)	(51.00)
Interest rate mark to market	(84.00)		(19.00)
Interest rate marrk-to-market Subtotal	(33.00)
Fair Value Inputs Level 3 [Member]
Fixed income [Abstract]
Total assets			194.00
Total liabilities	(289.00)		(127.00)
Total net assets	656.00		67.00
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Collateral received from counterparties, net of collateral paid to counterparties	(33.00)		8.00
Fair Value Inputs Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fixed income [Abstract]
Direct lending securities	183.00
Nuclear decommissioning trust fund investments subtotal	183.00	[2]	13.00	[2]
Fair Value Inputs Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fixed income [Abstract]
Residential mortgage-backed securities (non-agency)	89.00
Direct lending securities			37.00
Pledged assets for Zion Station decommissioning subtotal	89.00	[3]	37.00	[3]
Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Other investments	17.00
Total assets	945.00
Fair Value Inputs Level 3 [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	18.00		9.00
Fair value of energy swap contract noncurrent liability	49.00		97.00
Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Assets [Member]
Fixed income [Abstract]
Other derivatives	641.00		124.00
Proprietary trading	73.00		48.00
Effect of netting and allocation of collateral received/(paid)	(58.00)	[5]	(28.00)	[6]
Mark-to-market subtotal	656.00		144.00	[5]
Fair Value Inputs Level 3 [Member] | Commodity Mark To Market Derivative Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(236.00)		(119.00)
Proprietary trading	(78.00)		(28.00)
Effect of netting and allocation of collateral received/(paid)	25.00	[5]	20.00	[5]
Mark-to-market subtotal	(289.00)		(127.00)	[6]
Exelon Generation Co L L C [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)	334.00		103.00
Mark-to-market derivative liabilities (noncurrent liabilities)	232.00		29.00
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	245.00		562.00
Equity Securities [Abstract]
Equity securities	1,480.00		1,275.00
Commingled funds	1,933.00		1,822.00
Equity securities subtotal	3,413.00		3,097.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,057.00		1,047.00
Debt securities issued by states of the United States and political subdivisions of the states	321.00		541.00
Debt securities issued by foreign governments	93.00		16.00
Corporate debt securities	1,788.00		778.00
Federal agency mortgage-backed securities	24.00		357.00
Commercial mortgage-backed securities (non-agency)	45.00		83.00
Residential mortgage-backed securities (non-agency)	11.00		5.00
Mutual funds fixed income	23.00		47.00
Fixed income subtotal	3,362.00		2,874.00
Direct lending securities	183.00		13.00
Other debt obligations	15.00		18.00
Nuclear decommissioning trust fund investments subtotal	7,218.00		6,564.00
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	23.00
Equity Securities [Abstract]
Equity securities	14.00		35.00
Commingled funds	9.00		30.00
Equity securities subtotal	23.00		65.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	130.00		80.00
Debt securities issued by states of the United States and political subdivisions of the states	37.00		65.00
Corporate debt securities	249.00		314.00
Federal agency mortgage-backed securities	49.00		121.00
Commercial mortgage-backed securities (non-agency)	6.00		10.00
Commingled funds fixed income	0		20.00
Fixed income subtotal	471.00		610.00
Direct lending securities	89.00		37.00
Other debt obligations	1.00		13.00
Pledged assets for Zion Station decommissioning subtotal	607.00		725.00
Exelon Generation Co L L C [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	1.00
Fixed income [Abstract]
Mutual funds	13.00
Rabbi trust investments subtotal	14.00		4.00
Exelon Generation Co L L C [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	487.00		466.00
Fixed income [Abstract]
Cash flow hedges			1,551.00
Other derivatives	4,901.00		1,777.00
Proprietary trading	3,193.00		288.00
Effect of netting and allocation of collateral received/(paid)	6,056.00		1,855.00
Mark-to-market subtotal	2,038.00		1,761.00
Interest rate mark to market	50.00
Other investments	19.00
Total assets	10,433.00		9,520.00
Total net assets	9,839.00		9,370.00
Exelon Generation Co L L C [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges			(13.00)
Other derivatives	(3,499.00)		(1,151.00)
Proprietary trading	(3,121.00)		(264.00)
Effect of netting and allocation of collateral received/(paid)	6,087.00		1,315.00
Mark-to-market subtotal	(533.00)		(113.00)
Interest rate mark to market	(33.00)		(19.00)
Deferred compensation	(28.00)		18.00
Total liabilities	(594.00)		(150.00)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	28.00		(18.00)
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	245.00		562.00
Equity Securities [Abstract]
Equity securities	1,480.00		1,275.00
Equity securities subtotal	1,480.00		1,275.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,057.00		1,014.00
Fixed income subtotal	1,057.00		1,014.00
Nuclear decommissioning trust fund investments subtotal	2,782.00		2,851.00
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	14.00		35.00
Equity securities subtotal	14.00		35.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	118.00		54.00
Fixed income subtotal	118.00		54.00
Pledged assets for Zion Station decommissioning subtotal	132.00		89.00
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	1.00
Fixed income [Abstract]
Mutual funds	13.00
Rabbi trust investments subtotal	14.00		4.00
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	487.00		466.00
Fixed income [Abstract]
Other derivatives	861.00
Proprietary trading	1,042.00
Effect of netting and allocation of collateral received/(paid)	1,823.00
Mark-to-market subtotal	80.00
Other investments	2.00
Total assets	3,497.00		3,410.00
Total net assets	3,414.00		3,409.00
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(1,041.00)		(1.00)
Proprietary trading	(1,084.00)
Effect of netting and allocation of collateral received/(paid)	2,042.00
Mark-to-market subtotal	(83.00)		(1.00)
Total liabilities	(83.00)		(1.00)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Equity Securities [Abstract]
Commingled funds	1,933.00		1,822.00
Equity securities subtotal	1,933.00		1,822.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies			33.00
Debt securities issued by states of the United States and political subdivisions of the states	321.00		541.00
Debt securities issued by foreign governments	93.00		16.00
Corporate debt securities	1,788.00		778.00
Federal agency mortgage-backed securities	24.00		357.00
Commercial mortgage-backed securities (non-agency)	45.00		83.00
Residential mortgage-backed securities (non-agency)	11.00		5.00
Mutual funds fixed income	23.00		47.00
Fixed income subtotal	2,305.00		1,860.00
Other debt obligations	15.00		18.00
Nuclear decommissioning trust fund investments subtotal	4,253.00		3,700.00
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	23.00
Equity Securities [Abstract]
Commingled funds	9.00		30.00
Equity securities subtotal	9.00		30.00
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	12.00		26.00
Debt securities issued by states of the United States and political subdivisions of the states	37.00		65.00
Corporate debt securities	249.00		314.00
Federal agency mortgage-backed securities	49.00		121.00
Commercial mortgage-backed securities (non-agency)	6.00		10.00
Commingled funds fixed income	0		20.00
Fixed income subtotal	353.00		556.00
Other debt obligations	1.00		13.00
Pledged assets for Zion Station decommissioning subtotal	386.00		599.00
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges			857.00
Other derivatives	3,173.00		1,653.00
Proprietary trading	2,078.00		240.00
Effect of netting and allocation of collateral received/(paid)	4,175.00		1,827.00
Mark-to-market subtotal	1,076.00		923.00
Interest rate mark to market	50.00
Total assets	5,765.00		5,222.00
Total net assets	5,476.00		5,094.00
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges			(13.00)
Other derivatives	(2,289.00)		(1,137.00)
Proprietary trading	(1,959.00)		(236.00)
Effect of netting and allocation of collateral received/(paid)	4,020.00		1,295.00
Mark-to-market subtotal	(228.00)		(91.00)
Interest rate mark to market	(33.00)		(19.00)
Deferred compensation	(28.00)		18.00
Total liabilities	(289.00)		(128.00)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	28.00		(18.00)
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fixed income [Abstract]
Direct lending securities	183.00		13.00
Nuclear decommissioning trust fund investments subtotal	183.00		13.00
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	89.00		37.00
Pledged assets for Zion Station decommissioning subtotal	89.00		37.00
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges			694.00
Other derivatives	867.00		124.00
Proprietary trading	73.00		48.00
Effect of netting and allocation of collateral received/(paid)	58.00		28.00
Mark-to-market subtotal	882.00		838.00
Other investments	17.00
Total assets	1,171.00		888.00
Total net assets	949.00		867.00
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Other derivatives	(169.00)		(13.00)
Proprietary trading	(78.00)		(28.00)
Effect of netting and allocation of collateral received/(paid)	25.00		20.00
Mark-to-market subtotal	(222.00)		(21.00)
Total liabilities	(222.00)		(21.00)
Commonwealth Edison Co [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)	18.00		9.00
Mark-to-market derivative liabilities (noncurrent liabilities)	49.00		97.00
Commonwealth Edison Co [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents			2.00
Fixed income [Abstract]
Mutual funds	8.00		19.00
Rabbi trust investments subtotal	8.00		21.00
Commonwealth Edison Co [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	111.00		173.00
Fixed income [Abstract]
Total assets	119.00		194.00
Total net assets	(182.00)		(614.00)
Commonwealth Edison Co [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	(293.00)		(800.00)
Deferred compensation	8.00		8.00
Total liabilities	301.00		808.00
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(8.00)		(8.00)
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents			2.00
Fixed income [Abstract]
Mutual funds	8.00		19.00
Rabbi trust investments subtotal	8.00		21.00
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	111.00		173.00
Fixed income [Abstract]
Total assets	119.00		194.00
Total net assets	119.00		194.00
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Total net assets	(8.00)		(8.00)
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	8.00		8.00
Total liabilities	8.00		8.00
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(8.00)		(8.00)
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Total net assets	(293.00)		(800.00)
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	(293.00)		(800.00)
Total liabilities	293.00		800.00
PECO Energy Co [Member]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Mark-to-market derivative liabilities (current liabilities)	0		0
Mark-to-market derivative liabilities (noncurrent liabilities)	0		0
PECO Energy Co [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	9.00		9.00
PECO Energy Co [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	(346.00)		175.00
Fixed income [Abstract]
Total assets	355.00		184.00
Total net assets	337.00		163.00
PECO Energy Co [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	0
Deferred compensation	18.00		21.00
Total liabilities	18.00		21.00
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(18.00)		(21.00)
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	9.00
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	(346.00)		175.00
Fixed income [Abstract]
Total assets	355.00		184.00
Total net assets	355.00		184.00
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 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Total assets			0
Total net assets	(18.00)		(21.00)
PECO Energy Co [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	18.00		21.00
Total liabilities	18.00		21.00
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(18.00)		(21.00)
PECO Energy Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Total net assets	0
PECO Energy Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	0
Total liabilities	0
Baltimore Gas and Electric Company [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	5.00
Baltimore Gas and Electric Company [Member] | Derivative Financial Instruments Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	33.00		33.00
Fixed income [Abstract]
Total assets	38.00		33.00
Total net assets	33.00		33.00
Baltimore Gas and Electric Company [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	5.00
Total liabilities	5.00
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	(5.00)
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	5.00
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	33.00		33.00
Fixed income [Abstract]
Total assets	38.00		33.00
Total net assets	38.00		33.00
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Total net assets	(5.00)
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Deferred compensation	5.00
Total liabilities	5.00
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	$ (5.00)

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

[2] Excludes net assets (liabilities) of $30 million and $(57) million at December 31, 2012 and December 31, 2011, 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 and $9 million at December 31, 2012 and December 31, 2011, respectively. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.

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

[5] Excludes $28 million and $25 million of the cash surrender value of life insurance investments at December 31, 2012 and December 31, 2011, respectively.

[6] Includes collateral postings (received) from counterparties. Collateral (received) from counterparties, net of collateral paid to counterparties, totaled $219 million, $(155) million and $(33) million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2012. Collateral (received) from counterparties, net of collateral paid to counterparties, totaled $532 million and $8 million allocated to Level 2 and Level 3 mark-to-market derivatives, respectively, as of December 31, 2011.