Basis of Presentation (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011	Sep. 30, 2012		Sep. 30, 2011
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Current assets	$ 398,000,000			$ 398,000,000
Noncurrent assets	471,000,000			471,000,000
Total Assets	869,000,000			869,000,000
Current liabilities	269,000,000			269,000,000
Noncurrent liabilities	573,000,000			573,000,000
Total Liabilities	842,000,000			842,000,000
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	622,000,000	[1]		622,000,000	[1]
Total liabilities	312,000,000	[1]		312,000,000	[1]
Our ownership interest	98,000,000	[1]		98,000,000	[1]
Other ownership interests	212,000,000	[1]		212,000,000	[1]
Letter of Credit [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	8,000,000			8,000,000
Investments [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	78,000,000			78,000,000
Payment Guarantee [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	5,000,000			5,000,000
Power Contract Monetization Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	280,000,000	[1]		280,000,000	[1]
Total liabilities	217,000,000	[1]		217,000,000	[1]
Other ownership interests	63,000,000	[1]		63,000,000	[1]
Power Contract Monetization Entities [Member] | Letter of Credit [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	8,000,000			8,000,000
Other Than Power Contract Monetization Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	342,000,000	[1]		342,000,000	[1]
Total liabilities	95,000,000	[1]		95,000,000	[1]
Our ownership interest	98,000,000	[1]		98,000,000	[1]
Other ownership interests	149,000,000	[1]		149,000,000	[1]
Other Than Power Contract Monetization Entities [Member] | Investments [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	78,000,000			78,000,000
Other Than Power Contract Monetization Entities [Member] | Payment Guarantee [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	5,000,000			5,000,000
Exelon Generation Co L L C [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Current assets	348,000,000			348,000,000
Noncurrent assets	432,000,000			432,000,000
Total Assets	780,000,000			780,000,000
Current liabilities	193,000,000			193,000,000
Noncurrent liabilities	235,000,000			235,000,000
Total Liabilities	428,000,000			428,000,000
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Number of Variable Interest Entities not consolidated by equity holders	6			6
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	622,000,000	[1]		622,000,000	[1]
Total liabilities	312,000,000	[1]		312,000,000	[1]
Our ownership interest	98,000,000	[1]		98,000,000	[1]
Other ownership interests	212,000,000	[1]		212,000,000	[1]
Exelon Generation Co L L C [Member] | Letter of Credit [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	8,000,000			8,000,000
Exelon Generation Co L L C [Member] | Investments [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	78,000,000			78,000,000
Exelon Generation Co L L C [Member] | Payment Guarantee [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	5,000,000			5,000,000
Exelon Generation Co L L C [Member] | Power Contract Monetization Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	280,000,000	[1]		280,000,000	[1]
Total liabilities	217,000,000	[1]		217,000,000	[1]
Other ownership interests	63,000,000	[1]		63,000,000	[1]
Exelon Generation Co L L C [Member] | Power Contract Monetization Entities [Member] | Letter of Credit [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	8,000,000			8,000,000
Exelon Generation Co L L C [Member] | Other Than Power Contract Monetization Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	342,000,000	[1]		342,000,000	[1]
Total liabilities	95,000,000	[1]		95,000,000	[1]
Our ownership interest	98,000,000	[1]		98,000,000	[1]
Other ownership interests	149,000,000	[1]		149,000,000	[1]
Exelon Generation Co L L C [Member] | Other Than Power Contract Monetization Entities [Member] | Investments [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	78,000,000			78,000,000
Exelon Generation Co L L C [Member] | Other Than Power Contract Monetization Entities [Member] | Payment Guarantee [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	5,000,000			5,000,000
Exelon Generation Co L L C [Member] | Solar Project Limited Liability Companies [Member]
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Current assets	69,000,000			69,000,000
Noncurrent assets	516,000,000			516,000,000
Current liabilities	230,000,000			230,000,000
Noncurrent liabilities	159,000,000			159,000,000
Baltimore Gas and Electric Company [Member]
Consolidated Variable Interest Entity [Abstract]
Parental guarantee provided	75,000,000			75,000,000
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Current assets	49,000,000			49,000,000
Noncurrent assets	0			0
Total Assets	49,000,000			49,000,000
Current liabilities	75,000,000			75,000,000
Noncurrent liabilities	299,000,000			299,000,000
Total Liabilities	374,000,000			374,000,000
Baltimore Gas and Electric Company [Member] | RSB Bond Co LLC [Member]
Consolidated Variable Interest Entity [Abstract]
Remittance of payments received from customers for rate stabilization to BondCo.	$ 27,000,000		$ 27,000,000	$ 62,000,000		$ 65,000,000

[1] These items represent amounts on the unconsolidated VIE balance sheets, not on Exelon's or Generation's Consolidated Balance Sheets. These items are included to provide information regarding the relative size of the unconsolidated VIEs.