Fair Value of Financial Assets and Liabilities (Fair Value Inputs Assets Quantitative Information) (USD $)	6 Months Ended
	Jun. 30, 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	514,000,000	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	9,000,000	[1]
Forward gas price assets	2,750,000	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	67,000,000	[1]
Forward gas price assets	7,460,000	[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	25.00%	[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	304.00%	[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	(115,000,000)	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Proprietary Trading [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	15,000,000	[1]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Proprietary Trading [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Forward power price assets	75,000,000	[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	22.00%	[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	59.00%	[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	506,000,000	[2]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	7.90%	[2]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	9.50%	[2]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Net	(111,000,000)
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	3.50%
Forward heat rate	8	[3]
Renewable factor	88.00%
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	8.30%
Forward heat rate	9.5	[3]
Renewable factor	125.00%
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Net	506,000,000	[2]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	7.90%	[2]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Fair Value Inputs [Abstract]
Marketability Reserve	9.50%	[2]

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

[2] Includes current assets for Generation and current liabilities for ComEd of $506 million, 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.