Fair Value Quantitative Table (Details) (USD $)	3 Months Ended
	Mar. 31, 2012
Derivatives Fair Value [Line Items]
Forward Power Basis	4
Forward Gas Basis	0.25
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Net	682,000,000	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	14	[1]
Forward gas price assets	1.95	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	71	[1]
Forward gas price assets	3.08	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Volatility percentage	40.00%	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member] | Option Model Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Volatility percentage	60.00%	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Proprietary Trading [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Net	(145,000,000)	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price liabilities	17	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Proprietary Trading [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price liabilities	71	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Proprietary Trading [Member] | Option Model Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Volatility percentage	20.00%	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Proprietary Trading [Member] | Option Model Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Volatility percentage	60.00%	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Net	682,000,000	[2]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	8.20%	[2]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	10.80%	[2]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Net	(141,000,000)
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	3.50%
Forward heat rate	6.5	[3]
Renewable factor	84.00%
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	8.20%
Forward heat rate	8	[3]
Renewable factor	121.00%
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Net	682,000,000	[2]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member] | Discounted Cash Flow [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	8.20%	[2]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member] | Discounted Cash Flow [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	10.80%	[2]

[1] The valuation techniques, unobservable inputs and ranges are the same for the asset and liability positions.

[2] Includes current and noncurrent assets for Generation and current and noncurrent liabilities for ComEd of $590 million and $92 million, respectively, related to the fair value of the five-year financial swap contract between Generation and ComEd, which eliminates in consolidation.

[3] Quoted forward natural gas rates are utilized to project the forward power curve for the delivery of energy at specified future dates. The natural gas curve is extrapolated beyond its observable period to the end of the contract’s delivery.