Fair Value of Financial Assets and Liabilities (Fair Value Inputs Assets Quantitative Information) (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Derivatives Fair Value [Line Items]
Forward Power Basis	$ 3.83
Forward Gas Basis	0.37
Derivatives Fair Value Footnotes [Abstract]
Cash collateral excluded	118,000,000
Fair Value Inputs Level 3 [Member]
Derivatives Fair Value Footnotes [Abstract]
Cash collateral excluded			26,000,000
Exelon Generation Co L L C [Member]
Derivatives Fair Value Footnotes [Abstract]
Outstanding Commitments to invest	469,000,000
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	186,000,000	[1]	488,000,000	[2]
Derivatives Fair Value Footnotes [Abstract]
Fair value swap contract current asset			226,000,000
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	19,000,000		8,000,000	[3]
Forward gas price assets	2.18		2.98	[3]
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	155,000,000		176,000,000	[3]
Forward gas price assets	17.65		16.63	[3]
Renewable factor			128.00%
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	14.00%		15.00%	[3]
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	207.00%		142.00%	[3]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Proprietary Trading [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral			(3,000,000)	[2]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	17,000,000	[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 assets	(26,000,000)		(10,000,000)	[3]
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 assets	(152,000,000)		(176,000,000)	[3]
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	12.00%		14.00%	[3]
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%		19.00%	[3]
Exelon Generation Co L L C [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member]
Derivatives Fair Value Footnotes [Abstract]
Fair value swap contract current asset	0
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member]
Derivatives Fair Value [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	168,000,000	[1]
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Derivative [Member] | Discounted Cash Flow [Member]
Derivatives Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral			193,000,000	[2]
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%		3.50%
Forward heat rate	(8.00%)		(8.00%)	[4]
Renewable factor	87.00%		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	8.00%		8.00%
Forward heat rate	(9.00%)		(9.00%)	[4]
Renewable factor	127.00%
Commonwealth Edison Co [Member] | Fair Value Inputs Level 3 [Member] | Business Intersegment Transactions [Member]
Derivatives Fair Value Footnotes [Abstract]
Fair value swap contract current liability	$ 0

[1] The fair values do not include cash collateral held on level three positions of $118 million as of March 31, 2014. The upper ends of the ranges are driven by the winter power and gas prices in the New England region. Without the New England region, the upper ends of the ranges for power and gas would be approximately $114 and $10.62, respectively.

[2] The fair values do not include cash collateral held on level three positions of $26 million as of December 31, 2013 The upper ends of the ranges are driven by the winter power and gas prices in the New England region. Without the New England region, the upper ends of the ranges for power and gas would be approximately $100 and $5.70, respectively.

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

[4] 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.