Basis of Presentation (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011
Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net [Abstract]
Current assets	$ 355,000,000			$ 355,000,000
Noncurrent assets	446,000,000			446,000,000
Total Assets	801,000,000			801,000,000
Current liabilities	280,000,000			280,000,000
Noncurrent liabilities	553,000,000			553,000,000
Total Liabilities	833,000,000			833,000,000
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	646,000,000	[1]		646,000,000	[1]
Total liabilities	336,000,000	[1]		336,000,000	[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	11,000,000			11,000,000
Investments [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Our maximum exposure to loss	77,000,000			77,000,000
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	283,000,000	[1]		283,000,000	[1]
Total liabilities	220,000,000	[1]		220,000,000	[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	11,000,000			11,000,000
Other Than Power Contract Monetization Entities [Member]
Variable Interest Entity Nonconsolidated Carrying Amount Assets Liabilities And Other Information [Abstract]
Total assets	363,000,000	[1]		363,000,000	[1]
Total liabilities	116,000,000	[1]		116,000,000	[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	77,000,000			77,000,000
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	333,000,000			333,000,000
Noncurrent assets	403,000,000			403,000,000
Total Assets	736,000,000			736,000,000
Current liabilities	210,000,000			210,000,000
Noncurrent liabilities	212,000,000			212,000,000
Total Liabilities	422,000,000			422,000,000
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	646,000,000	[1]		646,000,000	[1]
Total liabilities	336,000,000	[1]		336,000,000	[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	11,000,000			11,000,000
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	77,000,000			77,000,000
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	283,000,000	[1]		283,000,000	[1]
Total liabilities	220,000,000	[1]		220,000,000	[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	11,000,000			11,000,000
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	363,000,000	[1]		363,000,000	[1]
Total liabilities	116,000,000	[1]		116,000,000	[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	77,000,000			77,000,000
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
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	22,000,000			22,000,000
Noncurrent assets	0			0
Total Assets	22,000,000			22,000,000
Current liabilities	70,000,000			70,000,000
Noncurrent liabilities	299,000,000			299,000,000
Total Liabilities	369,000,000			369,000,000
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.	$ 15,000,000		$ 16,000,000	$ 35,000,000		$ 39,000,000

[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.