Fair Value of Financial Assets and Liabilities (Details) (USD $)	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Dec. 31, 2011
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	$ 187,000,000	[1]			$ 861,000,000	[1]
Fixed income [Abstract]
Other investments	17,000,000
Deferred compensation	(106,000,000)				(73,000,000)
Total assets	10,778,000,000				9,268,000,000
Total liabilities	(1,883,000,000)				(311,000,000)
Total net assets	8,895,000,000				8,957,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	106,000,000				73,000,000
Mark-to-market derivative liabilities (current liabilities)	1,105,000,000				112,000,000
Mark-to-market derivative liabilities (noncurrent liabilities)	671,000,000				126,000,000
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	67,000,000		50,000,000
Total realized / unrealized gains (losses)
Included in income	85,000,000		(13,000,000)
Included in other comprehensive income			(9,000,000)
Included in regulatory assets	(35,000,000)		52,000,000
Change in collateral	(23,000,000)		5,000,000
Purchases, sales, issuances, and settlements
Purchases	336,000,000		31,000,000
Sales	(1,000,000)
Transfers out of Level 3 - (Asset) / Liability	(1,000,000)		(34,000,000)
Ending balance	428,000,000		82,000,000
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	93,000,000		(7,000,000)
Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	1,036,000,000				737,000,000
Long-term debt (including amounts due within one year)	17,545,000,000				12,627,000,000
Long-term debt to financing trusts	648,000,000				390,000,000
Spent nuclear fuel obligation	1,019,000,000				1,019,000,000
Preferred securities of subsidiary	87,000,000				87,000,000
Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities					737,000,000
Long-term debt (including amounts due within one year)					14,488,000,000
Long-term debt to financing trusts					358,000,000
Spent nuclear fuel obligation					886,000,000
Preferred securities of subsidiary					79,000,000
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	472,000,000
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	564,000,000
Long-term debt (including amounts due within one year)	18,918,000,000
Long-term debt to financing trusts	641,000,000
Spent nuclear fuel obligation	882,000,000
Preferred securities of subsidiary	79,000,000
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 3 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	162,000,000
Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance					13,000,000
Purchases, sales, issuances, and settlements
Ending balance	13,000,000				13,000,000
Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	37,000,000
Purchases, sales, issuances, and settlements
Purchases	6,000,000		31,000,000
Sales	(1,000,000)
Ending balance	42,000,000		31,000,000
Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	17,000,000		50,000,000
Total realized / unrealized gains (losses)
Included in income	85,000,000	[2]	(13,000,000)	[3]
Included in other comprehensive income			(9,000,000)	[4]
Included in regulatory assets	(35,000,000)	[5]	52,000,000	[6]
Change in collateral	(23,000,000)		5,000,000
Purchases, sales, issuances, and settlements
Purchases	316,000,000	[7]
Sales	0
Transfers out of Level 3 - (Asset) / Liability	(1,000,000)		(34,000,000)
Ending balance	359,000,000		51,000,000
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	93,000,000		(7,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Gain (loss) reclassified to results of operating due to the settlement of derivative contracts	(19,000,000)		(6,000,000)
Fair value of Constellation fair value assets acquired	310,000,000
Other Investments [Member]
Purchases, sales, issuances, and settlements
Purchases	14,000,000
Ending balance	14,000,000
Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	428,000,000				562,000,000
Equity Securities [Abstract]
Equity securities	1,460,000,000				1,275,000,000
Commingled funds	2,027,000,000				1,822,000,000
Equity securities subtotal	3,487,000,000				3,097,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	942,000,000				1,047,000,000
Debt securities issued by states of the United States and political subdivisions of the states	328,000,000				541,000,000
Debt securities issued by foreign governments	67,000,000				16,000,000
Corporate debt securities	1,534,000,000				778,000,000
Federal agency mortgage-backed securities	55,000,000				357,000,000
Commercial mortgage-backed securities (non-agency)	39,000,000				83,000,000
Residential mortgage-backed securities (non-agency)	8,000,000				5,000,000
Mutuall funds fixed income	2,000,000				47,000,000
Fixed income subtotal	2,975,000,000				2,874,000,000
Direct lending securities	13,000,000				13,000,000
Other debt obligations	11,000,000				18,000,000
Nuclear decommissioning trust fund investments subtotal	6,914,000,000	[8]			6,564,000,000	[8]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	13,000,000				(57,000,000)
Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	26,000,000				35,000,000
Commingled funds	22,000,000				30,000,000
Equity securities subtotal	48,000,000				65,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	87,000,000				80,000,000
Debt securities issued by states of the United States and political subdivisions of the states	53,000,000				65,000,000
Corporate debt securities	325,000,000				314,000,000
Federal agency mortgage-backed securities	100,000,000				121,000,000
Commercial mortgage-backed securities (non-agency)	10,000,000				10,000,000
Commingled funds fixed income	40,000,000				20,000,000
Fixed income subtotal	615,000,000				610,000,000
Direct lending securities	42,000,000				37,000,000
Other debt obligations	0				13,000,000
Pledged assets for Zion Station decommissioning subtotal	705,000,000	[9]			725,000,000	[9]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from pledged assets	3,000,000				9,000,000
Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	2,000,000				2,000,000
Fixed income [Abstract]
Mutual funds	73,000,000	[10],[11]			34,000,000	[10],[11]
Rabbi trust investments subtotal	75,000,000				36,000,000
Deferred compensation	(60,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	60,000,000
Supplemental executive retirement plan fair value	15,000,000
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	27,000,000				25,000,000
Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges	0				857,000,000
Other derivatives	9,891,000,000				1,777,000,000
Interest rate mark to market derivative assets	119,000,000				15,000,000
Proprietary trading	9,987,000,000				288,000,000
Effect of netting and allocation of collateral received/(paid)	(17,117,000,000)	[12]			(1,855,000,000)	[12]
Mark-to-market subtotal	2,761,000,000	[13]			1,067,000,000	[13]
Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges					(13,000,000)
Other derivatives	(8,635,000,000)				(1,257,000,000)
Interest rate mark to market derivative assets	(54,000,000)				(19,000,000)
Proprietary trading	(9,967,000,000)				(264,000,000)
Effect of netting and allocation of collateral received/(paid)	16,879,000,000	[12]			1,315,000,000	[12]
Mark-to-market subtotal	(1,723,000,000)	[13],[14]			(219,000,000)	[13],[14]
Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	187,000,000	[1]			861,000,000	[1]
Fixed income [Abstract]
Other investments	3,000,000
Deferred compensation	0				0
Total assets	3,183,046,165				3,837,000,000
Total liabilities	(229,087,424)				(1,000,000)
Total net assets	2,953,958,741				3,836,000,000
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	426,000,000
Fair Value Inputs Level 1 [Member] | Nuclear Decommissioning Trust Fund Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	428,000,000				562,000,000
Equity Securities [Abstract]
Equity securities	1,460,000,000				1,275,000,000
Commingled funds	0				0
Equity securities subtotal	1,460,000,000				1,275,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	941,000,000				1,014,000,000
Debt securities issued by states of the United States and political subdivisions of the states	0				0
Debt securities issued by foreign governments	0				0
Corporate debt securities	0				0
Federal agency mortgage-backed securities	0				0
Commercial mortgage-backed securities (non-agency)	0				0
Residential mortgage-backed securities (non-agency)	0				0
Mutuall funds fixed income	0				0
Fixed income subtotal	941,000,000				1,014,000,000
Direct lending securities	0				0
Other debt obligations	0				0
Nuclear decommissioning trust fund investments subtotal	2,829,000,000	[8]			2,851,000,000	[8]
Fair Value Inputs Level 1 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	26,000,000				35,000,000
Commingled funds	0				0
Equity securities subtotal	26,000,000				35,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	63,000,000				54,000,000
Debt securities issued by states of the United States and political subdivisions of the states	0				0
Corporate debt securities	0				0
Federal agency mortgage-backed securities	0				0
Commercial mortgage-backed securities (non-agency)	0				0
Commingled funds fixed income	0				0
Fixed income subtotal	63,000,000				54,000,000
Direct lending securities	0				0
Other debt obligations	0				0
Pledged assets for Zion Station decommissioning subtotal	89,000,000	[9]			89,000,000	[9]
Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	2,000,000				2,000,000
Fixed income [Abstract]
Mutual funds	73,000,000	[10],[11]			34,000,000	[10],[11]
Rabbi trust investments subtotal	75,000,000				36,000,000
Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges	0				0
Other derivatives	1,988,000,000				0
Interest rate mark to market derivative assets	0				0
Proprietary trading	3,341,000,000				0
Effect of netting and allocation of collateral received/(paid)	(5,328,953,835)	[12]			0	[12]
Mark-to-market subtotal	46,164.9999997462	[13]			0	[13]
Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges					0
Other derivatives	(2,527,000,000)				(1,000,000)
Interest rate mark to market derivative assets	0				0
Proprietary trading	(3,457,000,000)				0
Effect of netting and allocation of collateral received/(paid)	5,754,912,576	[12]			0	[12]
Mark-to-market subtotal	(229,087,424)	[13],[14]			(1,000,000)	[13],[14]
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]
Other investments	0
Deferred compensation	(106,000,000)				(73,000,000)
Total assets	6,686,953,835				5,237,000,000
Total liabilities	(1,173,912,576)				(183,000,000)
Total net assets	5,513,041,259				5,054,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	106,000,000				73,000,000
Collateral received from counterparties, net of collateral paid to counterparties	(627,000,000)				532,000,000
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				0
Equity Securities [Abstract]
Equity securities	0				0
Commingled funds	2,027,000,000				1,822,000,000
Equity securities subtotal	2,027,000,000				1,822,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,000,000				33,000,000
Debt securities issued by states of the United States and political subdivisions of the states	328,000,000				541,000,000
Debt securities issued by foreign governments	67,000,000				16,000,000
Corporate debt securities	1,534,000,000				778,000,000
Federal agency mortgage-backed securities	55,000,000				357,000,000
Commercial mortgage-backed securities (non-agency)	39,000,000				83,000,000
Residential mortgage-backed securities (non-agency)	8,000,000				5,000,000
Mutuall funds fixed income	2,000,000				47,000,000
Fixed income subtotal	2,034,000,000				1,860,000,000
Direct lending securities	0				0
Other debt obligations	11,000,000				18,000,000
Nuclear decommissioning trust fund investments subtotal	4,072,000,000	[8]			3,700,000,000	[8]
Fair Value Inputs Level 2 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	0				0
Commingled funds	22,000,000				30,000,000
Equity securities subtotal	22,000,000				30,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	24,000,000				26,000,000
Debt securities issued by states of the United States and political subdivisions of the states	53,000,000				65,000,000
Corporate debt securities	325,000,000				314,000,000
Federal agency mortgage-backed securities	100,000,000				121,000,000
Commercial mortgage-backed securities (non-agency)	10,000,000				10,000,000
Commingled funds fixed income	40,000,000				20,000,000
Fixed income subtotal	552,000,000				556,000,000
Direct lending securities	0				0
Other debt obligations	0				13,000,000
Pledged assets for Zion Station decommissioning subtotal	574,000,000	[9]			599,000,000	[9]
Fair Value Inputs Level 2 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0				0
Fixed income [Abstract]
Mutual funds	0	[10],[11]			0	[10],[11]
Rabbi trust investments subtotal	0				0
Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges	0				857,000,000
Other derivatives	6,913,000,000				1,653,000,000
Interest rate mark to market derivative assets	119,000,000				15,000,000
Proprietary trading	6,427,000,000				240,000,000
Effect of netting and allocation of collateral received/(paid)	(11,418,046,165)	[12]			(1,827,000,000)	[12]
Mark-to-market subtotal	1,921,953,835	[13]			923,000,000	[13]
Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges					(13,000,000)
Other derivatives	(5,659,000,000)				(1,137,000,000)
Interest rate mark to market derivative assets	(54,000,000)				(19,000,000)
Proprietary trading	(6,146,000,000)				(236,000,000)
Effect of netting and allocation of collateral received/(paid)	10,791,087,424	[12]			1,295,000,000	[12]
Mark-to-market subtotal	(1,013,912,576)	[13],[14]			(91,000,000)	[13],[14]
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	14,000,000
Deferred compensation	0				0
Total assets	908,000,000				194,000,000
Total liabilities	(480,000,000)				(127,000,000)
Total net assets	428,000,000				67,000,000
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	(37,000,000)				8,000,000
Mark-to-market derivative liabilities (current liabilities)	16,000,000				9,000,000
Mark-to-market derivative liabilities (noncurrent liabilities)	125,000,000				97,000,000
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				0
Equity Securities [Abstract]
Equity securities	0				0
Commingled funds	0				0
Equity securities subtotal	0				0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0				0
Debt securities issued by states of the United States and political subdivisions of the states	0				0
Debt securities issued by foreign governments	0				0
Corporate debt securities	0				0
Federal agency mortgage-backed securities	0				0
Commercial mortgage-backed securities (non-agency)	0				0
Residential mortgage-backed securities (non-agency)	0				0
Mutuall funds fixed income	0				0
Fixed income subtotal	0				0
Direct lending securities	13,000,000				13,000,000
Other debt obligations	0				0
Nuclear decommissioning trust fund investments subtotal	13,000,000	[8]			13,000,000	[8]
Fair Value Inputs Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	0				0
Commingled funds	0				0
Equity securities subtotal	0				0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0				0
Debt securities issued by states of the United States and political subdivisions of the states	0				0
Corporate debt securities	0				0
Federal agency mortgage-backed securities	0				0
Commercial mortgage-backed securities (non-agency)	0				0
Commingled funds fixed income	0				0
Fixed income subtotal	0				0
Direct lending securities	42,000,000				37,000,000
Other debt obligations	0				0
Pledged assets for Zion Station decommissioning subtotal	42,000,000	[9]			37,000,000	[9]
Fair Value Inputs Level 3 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0				0
Fixed income [Abstract]
Mutual funds	0	[10],[11]			0	[10],[11]
Rabbi trust investments subtotal	0				0
Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges	0				0
Other derivatives	990,000,000				124,000,000
Interest rate mark to market derivative assets	0				0
Proprietary trading	219,000,000				48,000,000
Effect of netting and allocation of collateral received/(paid)	(370,000,000)	[12]			(28,000,000)	[12]
Mark-to-market subtotal	839,000,000	[13]			144,000,000	[13]
Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges					0
Other derivatives	(449,000,000)				(119,000,000)
Interest rate mark to market derivative assets	0				0
Proprietary trading	(364,000,000)				(28,000,000)
Effect of netting and allocation of collateral received/(paid)	333,000,000	[12]			20,000,000	[12]
Mark-to-market subtotal	(480,000,000)	[13],[14]			(127,000,000)	[13],[14]
Operating Revenue [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Total gains (losses) included in income	87,000,000		(3,000,000)
Change in the unrealized gains (losses) relating to assets and liabilities held	104,000,000		4,000,000
Purchased Fuel and Electric [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Total gains (losses) included in income	(2,000,000)		(10,000,000)
Change in the unrealized gains (losses) relating to assets and liabilities held	(11,000,000)		(11,000,000)
Exelon Generation Co L L C [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	60,000,000	[1]			466,000,000	[1]
Fixed income [Abstract]
Other investments	17,000,000
Deferred compensation	(20,000,000)				(18,000,000)
Total assets	11,249,000,000				9,520,000,000
Total liabilities	(1,656,000,000)				(150,000,000)
Total net assets	9,593,000,000				9,370,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	20,000,000				18,000,000
Fair value swap contract current asset	590,000,000				503,000,000
Fair value swap contract noncurrent asset	92,000,000				191,000,000
Mark-to-market derivative liabilities (current liabilities)	1,090,000,000				103,000,000
Mark-to-market derivative liabilities (noncurrent liabilities)	546,000,000				29,000,000
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	867,000,000		1,030,000,000
Total realized / unrealized gains (losses)
Included in income	74,000,000		(13,000,000)
Included in other comprehensive income	(1,000,000)		(55,000,000)
Change in collateral	(23,000,000)		5,000,000
Purchases, sales, issuances, and settlements
Purchases	336,000,000		31,000,000
Sales	(1,000,000)
Transfers out of Level 3 - (Asset) / Liability	(1,000,000)		(34,000,000)
Ending balance	1,251,000,000		964,000,000
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	93,000,000		(7,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Increase (decrease) in fair value related to the swap contract			(67,000,000)
Increase (decrease) in fair value related to block contracts			1,000,000
Increase (decrease) in fair value related to floating-to-fixed energy swap contracts			(51,000,000)
Exelon Generation Co L L C [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	114,000,000				2,000,000
Long-term debt (including amounts due within one year)	6,646,000,000				3,677,000,000
Spent nuclear fuel obligation	1,019,000,000				1,019,000,000
Exelon Generation Co L L C [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities					2,000,000
Long-term debt (including amounts due within one year)					4,231,000,000
Spent nuclear fuel obligation					886,000,000
Exelon Generation Co L L C [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	0
Long-term debt (including amounts due within one year)	0
Spent nuclear fuel obligation	0
Exelon Generation Co L L C [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	114,000,000
Long-term debt (including amounts due within one year)	6,804,000,000
Spent nuclear fuel obligation	882,000,000
Exelon Generation Co L L C [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 3 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	0
Long-term debt (including amounts due within one year)	67,000,000
Spent nuclear fuel obligation	0
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance					13,000,000
Purchases, sales, issuances, and settlements
Ending balance	13,000,000				13,000,000
Exelon Generation Co L L C [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	37,000,000
Purchases, sales, issuances, and settlements
Purchases	6,000,000		31,000,000
Sales	(1,000,000)
Transfers out of Level 3 - (Asset) / Liability	0
Ending balance	42,000,000		31,000,000
Exelon Generation Co L L C [Member] | Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	817,000,000		1,030,000,000
Total realized / unrealized gains (losses)
Included in income	74,000,000	[2]	(13,000,000)	[15]
Included in other comprehensive income	(1,000,000)	[5]	(55,000,000)	[16]
Change in collateral	(23,000,000)		5,000,000
Purchases, sales, issuances, and settlements
Purchases	316,000,000	[17]
Transfers out of Level 3 - (Asset) / Liability	(1,000,000)		(34,000,000)
Ending balance	1,182,000,000		933,000,000
The amount of total gains (losses) included in income attributed to the change in unrealized gains (losses) related to assets and liabilities	93,000,000		(7,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Gain (loss) reclassified to results of operating due to the settlement of derivative contracts	(19,000,000)		(6,000,000)
Increase (decrease) in fair value related to the swap contract	135,000,000		(112,000,000)
Realized gains (losses) related to swap contract	(147,000,000)
Fair value of Constellation fair value assets acquired	310,000,000
Exelon Generation Co L L C [Member] | Other Investments [Member]
Purchases, sales, issuances, and settlements
Purchases	14,000,000
Ending balance	14,000,000
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	428,000,000				562,000,000
Equity Securities [Abstract]
Equity securities	1,460,000,000				1,275,000,000
Commingled funds	2,027,000,000				1,822,000,000
Equity securities subtotal	3,487,000,000				3,097,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	942,000,000				1,047,000,000
Debt securities issued by states of the United States and political subdivisions of the states	328,000,000				541,000,000
Debt securities issued by foreign governments	67,000,000				16,000,000
Corporate debt securities	1,534,000,000				778,000,000
Federal agency mortgage-backed securities	55,000,000				357,000,000
Commercial mortgage-backed securities (non-agency)	39,000,000				83,000,000
Residential mortgage-backed securities (non-agency)	8,000,000				5,000,000
Mutuall funds fixed income	2,000,000				47,000,000
Fixed income subtotal	2,975,000,000				2,874,000,000
Direct lending securities	13,000,000				13,000,000
Other debt obligations	11,000,000				18,000,000
Nuclear decommissioning trust fund investments subtotal	6,914,000,000	[8]			6,564,000,000	[8]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from nuclear decommissioning trust fund investments	13,000,000				(57,000,000)
Exelon Generation Co L L C [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	26,000,000				35,000,000
Commingled funds	22,000,000				30,000,000
Equity securities subtotal	48,000,000				65,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	87,000,000				80,000,000
Debt securities issued by states of the United States and political subdivisions of the states	53,000,000				65,000,000
Corporate debt securities	325,000,000				314,000,000
Federal agency mortgage-backed securities	100,000,000				121,000,000
Commercial mortgage-backed securities (non-agency)	10,000,000				10,000,000
Commingled funds fixed income	40,000,000				20,000,000
Fixed income subtotal	615,000,000				610,000,000
Direct lending securities	42,000,000				37,000,000
Other debt obligations	0				13,000,000
Pledged assets for Zion Station decommissioning subtotal	705,000,000	[18]			725,000,000	[18]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Net assets (liabilities) excluded from pledged assets	3,000,000				9,000,000
Exelon Generation Co L L C [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	5,000,000	[19],[20]			4,000,000	[19],[20]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	7,000,000				7,000,000
Exelon Generation Co L L C [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges					1,551,000,000
Other derivatives	10,573,000,000				1,777,000,000
Interest rate mark to market derivative assets	105,000,000
Proprietary trading	9,987,000,000				288,000,000
Effect of netting and allocation of collateral received/(paid)	(17,117,000,000)	[12]			(1,855,000,000)	[12]
Mark-to-market subtotal	3,443,000,000	[21]			1,761,000,000	[21]
Exelon Generation Co L L C [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges					(13,000,000)
Other derivatives	(8,494,000,000)				(1,151,000,000)
Interest rate mark to market derivative assets	(54,000,000)				(19,000,000)
Proprietary trading	(9,967,000,000)				(264,000,000)
Effect of netting and allocation of collateral received/(paid)	16,879,000,000	[12]			1,315,000,000	[12]
Mark-to-market subtotal	(1,582,000,000)				(113,000,000)
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	60,000,000	[1]			466,000,000	[1]
Fixed income [Abstract]
Other investments	3,000,000
Deferred compensation	0				0
Total assets	2,986,046,165				3,410,000,000
Total liabilities	(229,087,424)				(1,000,000)
Total net assets	2,756,958,741				3,409,000,000
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	426,000,000
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	428,000,000				562,000,000
Equity Securities [Abstract]
Equity securities	1,460,000,000				1,275,000,000
Commingled funds	0				0
Equity securities subtotal	1,460,000,000				1,275,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	941,000,000				1,014,000,000
Debt securities issued by states of the United States and political subdivisions of the states	0				0
Debt securities issued by foreign governments	0				0
Corporate debt securities	0				0
Federal agency mortgage-backed securities	0				0
Commercial mortgage-backed securities (non-agency)	0				0
Residential mortgage-backed securities (non-agency)	0				0
Mutuall funds fixed income	0				0
Fixed income subtotal	941,000,000				1,014,000,000
Direct lending securities	0				0
Other debt obligations	0				0
Nuclear decommissioning trust fund investments subtotal	2,829,000,000	[8]			2,851,000,000	[8]
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	26,000,000				35,000,000
Commingled funds	0				0
Equity securities subtotal	26,000,000				35,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	63,000,000				54,000,000
Debt securities issued by states of the United States and political subdivisions of the states	0				0
Corporate debt securities	0				0
Federal agency mortgage-backed securities	0				0
Commercial mortgage-backed securities (non-agency)	0				0
Commingled funds fixed income	0				0
Fixed income subtotal	63,000,000				54,000,000
Direct lending securities	0				0
Other debt obligations	0				0
Pledged assets for Zion Station decommissioning subtotal	89,000,000	[18]			89,000,000	[18]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	5,000,000	[19],[20]			4,000,000	[19],[20]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges					0
Other derivatives	1,988,000,000				0
Interest rate mark to market derivative assets	0
Proprietary trading	3,341,000,000				0
Effect of netting and allocation of collateral received/(paid)	(5,328,953,835)	[12]			0	[12]
Mark-to-market subtotal	46,164.9999997462	[21]			0	[21]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges					0
Other derivatives	(2,527,000,000)				(1,000,000)
Interest rate mark to market derivative assets	0				0
Proprietary trading	(3,457,000,000)				0
Effect of netting and allocation of collateral received/(paid)	5,754,912,576	[12]			0	[12]
Mark-to-market subtotal	(229,087,424)				(1,000,000)
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	[1]			0	[1]
Fixed income [Abstract]
Other investments	0
Deferred compensation	(20,000,000)				(18,000,000)
Total assets	6,672,953,835				5,222,000,000
Total liabilities	(1,087,912,576)				(128,000,000)
Total net assets	5,585,041,259				5,094,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	20,000,000				18,000,000
Collateral received from counterparties, net of collateral paid to counterparties	(627,000,000)				532,000,000
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				0
Equity Securities [Abstract]
Equity securities	0				0
Commingled funds	2,027,000,000				1,822,000,000
Equity securities subtotal	2,027,000,000				1,822,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	1,000,000				33,000,000
Debt securities issued by states of the United States and political subdivisions of the states	328,000,000				541,000,000
Debt securities issued by foreign governments	67,000,000				16,000,000
Corporate debt securities	1,534,000,000				778,000,000
Federal agency mortgage-backed securities	55,000,000				357,000,000
Commercial mortgage-backed securities (non-agency)	39,000,000				83,000,000
Residential mortgage-backed securities (non-agency)	8,000,000				5,000,000
Mutuall funds fixed income	2,000,000				47,000,000
Fixed income subtotal	2,034,000,000				1,860,000,000
Direct lending securities	0				0
Other debt obligations	11,000,000				18,000,000
Nuclear decommissioning trust fund investments subtotal	4,072,000,000	[8]			3,700,000,000	[8]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	0				0
Commingled funds	22,000,000				30,000,000
Equity securities subtotal	22,000,000				30,000,000
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	24,000,000				26,000,000
Debt securities issued by states of the United States and political subdivisions of the states	53,000,000				65,000,000
Corporate debt securities	325,000,000				314,000,000
Federal agency mortgage-backed securities	100,000,000				121,000,000
Commercial mortgage-backed securities (non-agency)	10,000,000				10,000,000
Commingled funds fixed income	40,000,000				20,000,000
Fixed income subtotal	552,000,000				556,000,000
Direct lending securities	0				0
Other debt obligations	0				13,000,000
Pledged assets for Zion Station decommissioning subtotal	574,000,000	[18]			599,000,000	[18]
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	[19],[20]			0	[19],[20]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges					857,000,000
Other derivatives	6,913,000,000				1,653,000,000
Interest rate mark to market derivative assets	105,000,000
Proprietary trading	6,427,000,000				240,000,000
Effect of netting and allocation of collateral received/(paid)	(11,418,046,165)	[12]			(1,827,000,000)	[12]
Mark-to-market subtotal	1,921,953,835	[21]			923,000,000	[21]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges					(13,000,000)
Other derivatives	(5,659,000,000)				(1,137,000,000)
Interest rate mark to market derivative assets	(54,000,000)				(19,000,000)
Proprietary trading	(6,146,000,000)				(236,000,000)
Effect of netting and allocation of collateral received/(paid)	10,791,087,424	[12]			1,295,000,000	[12]
Mark-to-market subtotal	(1,013,912,576)				(91,000,000)
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	[1]			0	[1]
Fixed income [Abstract]
Other investments	14,000,000
Deferred compensation	0				0
Total assets	1,590,000,000				888,000,000
Total liabilities	(339,000,000)				(21,000,000)
Total net assets	1,251,000,000				867,000,000
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	(37,000,000)				8,000,000
Exelon Generation Co L L C [Member] | 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				0
Equity Securities [Abstract]
Equity securities	0				0
Commingled funds	0				0
Equity securities subtotal	0				0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0				0
Debt securities issued by states of the United States and political subdivisions of the states	0				0
Debt securities issued by foreign governments	0				0
Corporate debt securities	0				0
Federal agency mortgage-backed securities	0				0
Commercial mortgage-backed securities (non-agency)	0				0
Residential mortgage-backed securities (non-agency)	0				0
Mutuall funds fixed income	0				0
Fixed income subtotal	0				0
Direct lending securities	13,000,000				13,000,000
Other debt obligations	0				0
Nuclear decommissioning trust fund investments subtotal	13,000,000	[8]			13,000,000	[8]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Pledged Assets For Zion Station Decommissioning [Member]
Equity Securities [Abstract]
Equity securities	0				0
Commingled funds	0				0
Equity securities subtotal	0				0
Fixed income [Abstract]
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies	0				0
Debt securities issued by states of the United States and political subdivisions of the states	0				0
Corporate debt securities	0				0
Federal agency mortgage-backed securities	0				0
Commercial mortgage-backed securities (non-agency)	0				0
Commingled funds fixed income	0				0
Fixed income subtotal	0				0
Direct lending securities	42,000,000				37,000,000
Other debt obligations	0				0
Pledged assets for Zion Station decommissioning subtotal	42,000,000	[18]			37,000,000	[18]
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	[19],[20]			0	[19],[20]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Cash flow hedges					694,000,000
Other derivatives	1,672,000,000				124,000,000
Interest rate mark to market derivative assets	0
Proprietary trading	219,000,000				48,000,000
Effect of netting and allocation of collateral received/(paid)	(370,000,000)	[12]			(28,000,000)	[12]
Mark-to-market subtotal	1,521,000,000	[21]			838,000,000	[21]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Cash flow hedges					0
Other derivatives	(308,000,000)				(13,000,000)
Interest rate mark to market derivative assets	0				0
Proprietary trading	(364,000,000)				(28,000,000)
Effect of netting and allocation of collateral received/(paid)	333,000,000	[12]			20,000,000	[12]
Mark-to-market subtotal	(339,000,000)				(21,000,000)
Exelon Generation Co L L C [Member] | Operating Revenue [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Gain Loss Included In Earnings [Line Items]
Total gains (losses) included in income	76,000,000		(3,000,000)
Change in the unrealized gains (losses) relating to assets and liabilities held	104,000,000		4,000,000
Commonwealth Edison Co [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	3,000,000	[1]			173,000,000	[1]
Fixed income [Abstract]
Deferred compensation	(9,000,000)				(8,000,000)
Total assets	19,000,000				194,000,000
Total liabilities	(832,000,000)				(808,000,000)
Total net assets	(813,000,000)				(614,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	9,000,000				8,000,000
Fair value swap contract current liability	590,000,000				503,000,000
Fair value swap contract noncurrent liability	92,000,000				191,000,000
Mark-to-market derivative liabilities (noncurrent liabilities)	125,000,000				97,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Increase (decrease) in fair value related to the swap contract			67,000,000
Increase (decrease) in fair value related to floating-to-fixed energy swap contracts			51,000,000
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	6,067,000,000
Long-term debt to financing trusts	206,000,000
Commonwealth Edison Co [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	302,000,000
Long-term debt (including amounts due within one year)	5,215,000,000				5,665,000,000
Long-term debt to financing trusts	206,000,000				206,000,000
Commonwealth Edison Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)					6,540,000,000
Long-term debt to financing trusts					184,000,000
Commonwealth Edison Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	302,000,000
Commonwealth Edison Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 3 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	18,000,000
Commonwealth Edison Co [Member] | Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance	(800,000,000)		(971,000,000)
Total realized / unrealized gains (losses)
Included in regulatory assets	(23,000,000)	[22],[6]	96,000,000	[22],[6]
Purchases, sales, issuances, and settlements
Ending balance	(823,000,000)		(875,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Increase (decrease) in fair value related to the swap contract	(135,000,000)		112,000,000
Realized gains (losses) related to swap contract	147,000,000
Increase (decrease) in fair value related to floating-to-fixed energy swap contracts	35,000,000
Commonwealth Edison Co [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	1,000,000				2,000,000
Fixed income [Abstract]
Mutual funds	15,000,000				19,000,000
Rabbi trust investments subtotal	16,000,000				21,000,000
Commonwealth Edison Co [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Mark-to-market subtotal					0
Commonwealth Edison Co [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	(823,000,000)	[14],[23]			(800,000,000)	[14],[23]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	3,000,000	[1]			173,000,000	[1]
Fixed income [Abstract]
Deferred compensation	0				0
Total assets	19,000,000				194,000,000
Total liabilities	0				0
Total net assets	19,000,000				194,000,000
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]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	1,000,000				2,000,000
Fixed income [Abstract]
Mutual funds	15,000,000				19,000,000
Rabbi trust investments subtotal	16,000,000				21,000,000
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Mark-to-market subtotal					0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 1 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	0	[14],[23]			0	[14],[23]
Commonwealth Edison Co [Member] | 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	(9,000,000)				(8,000,000)
Total assets	0				0
Total liabilities	(9,000,000)				(8,000,000)
Total net assets	(9,000,000)				(8,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	9,000,000				8,000,000
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0				0
Fixed income [Abstract]
Mutual funds	0				0
Rabbi trust investments subtotal	0				0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Mark-to-market subtotal					0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 2 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	0	[14],[23]			0	[14],[23]
Commonwealth Edison Co [Member] | 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]
Deferred compensation	0				0
Total assets	0				0
Total liabilities	(823,000,000)				(800,000,000)
Total net assets	(823,000,000)				(800,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0				0
Mark-to-market derivative liabilities (current liabilities)	16,000,000				9,000,000
Mark-to-market derivative liabilities (noncurrent liabilities)	125,000,000				97,000,000
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Rabbi Trust Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0				0
Fixed income [Abstract]
Mutual funds	0				0
Rabbi trust investments subtotal	0				0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Assets [Member]
Fixed income [Abstract]
Mark-to-market subtotal					0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative Financial Instruments Liabilities [Member]
Fixed income [Abstract]
Mark-to-market subtotal	(823,000,000)	[14],[23]			(800,000,000)	[14],[23]
PECO Energy Co [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	53,000,000				175,000,000	[1]
Fixed income [Abstract]
Deferred compensation	(21,000,000)				(21,000,000)
Total assets	62,000,000				184,000,000
Total liabilities	(21,000,000)				(21,000,000)
Total net assets	41,000,000				163,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	21,000,000				21,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Increase (decrease) in fair value related to block contracts			(1,000,000)
PECO Energy Co [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	225,000,000				225,000,000
Long-term debt (including amounts due within one year)	1,972,000,000				1,972,000,000
Long-term debt to financing trusts	184,000,000				184,000,000
Preferred securities of subsidiary	87,000,000				87,000,000
PECO Energy Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities					225,000,000
Long-term debt (including amounts due within one year)					2,295,000,000
Long-term debt to financing trusts					174,000,000
Preferred securities of subsidiary					79,000,000
PECO Energy Co [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Short-term liabilities	225,000,000
Long-term debt (including amounts due within one year)	2,291,498,750
Long-term debt to financing trusts	176,000,000
Preferred securities of subsidiary	79,000,000
PECO Energy Co [Member] | Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Beginning balance			(9,000,000)
Total realized / unrealized gains (losses)
Included in regulatory assets			2,000,000	[24]
Purchases, sales, issuances, and settlements
Ending balance			(7,000,000)
PECO Energy Co [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal	9,000,000	[25],[26]			9,000,000	[25],[26]
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash surrender value of life insurance investments excluded from Rabbi Trust investments	14,000,000				13,000,000
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	53,000,000				175,000,000	[1]
Fixed income [Abstract]
Deferred compensation	0				0
Total assets	62,000,000				184,000,000
Total liabilities	0				0
Total net assets	62,000,000				184,000,000
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	0				0
PECO Energy Co [Member] | Fair Value Inputs Level 1 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Mutual funds	9,000,000	[25],[26]
Rabbi trust investments subtotal	0	[25],[26]			9,000,000	[25],[26]
PECO Energy Co [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	(21,000,000)				(21,000,000)
Total assets	0				0
Total liabilities	(21,000,000)				(21,000,000)
Total net assets	(21,000,000)				(21,000,000)
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Deferred compensation	21,000,000				21,000,000
PECO Energy Co [Member] | Fair Value Inputs Level 2 [Member] | Rabbi Trust Investments [Member]
Fixed income [Abstract]
Rabbi trust investments subtotal					0	[25],[26]
PECO Energy Co [Member] | Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	0				0	[1]
Fixed income [Abstract]
Deferred compensation	0				0
Total assets	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 [Abstract]
Rabbi trust investments subtotal	0	[25],[26]			0	[25],[26]
Baltimore Gas and Electric Company [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	2,101,000,000				2,101,000,000
Long-term debt to financing trusts	258,000,000				258,000,000
Baltimore Gas and Electric Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)					2,377,000,000
Long-term debt to financing trusts					256,000,000
Baltimore Gas and Electric Company [Member] | Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	2,359,000,000
Long-term debt to financing trusts	259,000,000
Baltimore Gas and Electric Company [Member] | Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Cash equivalents	$ 52,000,000

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

[2] Includes the reclassification of $19 million of realized losses due to the settlement of derivative contracts recorded in results of operations.

[3] Includes the reclassification of $6 million of realized losses due to the settlement of derivative contracts recorded in results of operations.

[4] Excludes $67 million of changes in fair value and $112 million of realized losses due to settlements associated with Generation's financial swap contract with ComEd and a $1 million decrease related to the settlement of Generation’s block contracts with PECO, which eliminates upon consolidation in Exelon's Consolidated Financial Statements.

[5] Includes $135 million of increases in fair value and $147 million of realized losses due to settlements during 2012 of Generation's financial swap contract with ComEd, which eliminates upon consolidation in Exelon's Consolidated Financial Statements.

[6] Includes an increase in fair value of $51 million associated with floating-to-fixed energy swap contracts with unaffiliated suppliers.

[7] Includes $310 million of fair value from contracts and $14 million of other investments acquired as a result of the merger.

[8] Excludes net assets (liabilities) of $13 million and $(57) million at March 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.

[9] Excludes net assets of $3 million and $9 million at March 31, 2012 and December 31, 2011. These items consist of receivables related to pending securities sales, interest and dividend receivables, and payables related to pending securities purchases.

[10] Excludes $27 million and $25 million of the cash surrender value of life insurance investments at March 31, 2012 and December 31, 2011, respectively.

[11] The mutual funds held by the Rabbi trusts include $60 million related to deferred compensation and $15 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.

[12] Includes collateral postings received from counterparties. Collateral received from counterparties, net of collateral paid to counterparties, totaled $426, $(627) million and $(37) million allocated to Level 1, Level 2 and Level 3 mark-to-market derivatives, respectively, as of March 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.

[13] The Level 3 balance does not include current and noncurrent assets for Generation and current and noncurrent liabilities for ComEd of $590 million and $92 million at March 31, 2012 and $503 million and $191 million at December 31, 2011, respectively, related to the fair value of Generation's financial swap contract with ComEd.

[14] The Level 3 balance includes the current and noncurrent liability of $ 16 million and $125 million at March 31, 2012, respectively, and $9 million and $97 million at December 31, 2011, respectively, related to floating-to-fixed energy swap contracts with unaffiliated suppliers.

[15] Includes the reclassification of $6 million of realized gains due to the settlement of derivative contracts recorded in results of operations.

[16] Includes $67 million changes in fair value and $112 million of realized losses due to settlements during 2011 of Generation's financial swap contract with ComEd and $1 million of changes in the fair value of Generation's block contract with PECO, which eliminates upon consolidation in Exelon's Consolidated Financial Statements.

[17] Includes $310 million of fair value from contracts and $14 million of other investments acquired as a result of the merger

[18] Excludes net assets of $3 million and $9 million at March 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.

[19] The mutual funds held by the Rabbi trusts are classified as Level 1 as they are valued based upon quoted prices (unadjusted) in active markets.

[20] Excludes $7 million and $7 million of the cash surrender value of life insurance investments at March 31, 2012 and December 31, 2011, respectively.

[21] The Level 3 balance includes current and noncurrent assets for Generation of $590 million and $92 million at March 31, 2012 and $503 million and $191 million at December 31, 2011, respectively, related to the fair value of Generation's financial swap contract with ComEd, which eliminates upon consolidation in Exelon's Consolidated Financial Statements.

[22] Includes $67 million of changes in the fair value and $112 million of realized gains due to settlements associated with ComEd's financial swap with Generation. All items eliminate upon consolidation in Exelon's Consolidated Financial Statements.

[23] The Level 3 balance includes the current and noncurrent liability of $590 million and $92 million at March 31, 2012, respectively, and $503 million and $191 million at December 31, 2011, respectively, related to the fair value of ComEd's financial swap contract with Generation which eliminates upon consolidation in Exelon's Consolidated Financial Statements.

[24] Includes a $1 million increase related to the settlement of PECO's block contract with Generation, which eliminates upon consolidation in Exelon's Consolidated Financial Statements.

[25] The mutual funds held by the Rabbi trusts are classified as Level 1 as they are valued based upon quoted prices (unadjusted) in active markets

[26] Excludes $14 million and $13 million of the cash surrender value of life insurance investments at March 31, 2012 and December 31, 2011, respectively.