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Fair Value of Financial Assets and Liabilities (Fair Value Inputs Assets Quantitative Information) (Details) (USD $)
 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended 12 Months Ended
Dec. 31, 2012
Derivative [Member]
Discounted Cash Flow [Member]
Dec. 31, 2012
Derivative [Member]
Discounted Cash Flow [Member]
Minimum [Member]
Dec. 31, 2012
Derivative [Member]
Discounted Cash Flow [Member]
Maximum [Member]
Dec. 31, 2012
Exelon Generation Co L L C [Member]
Discounted Cash Flow [Member]
Minimum [Member]
Dec. 31, 2012
Exelon Generation Co L L C [Member]
Discounted Cash Flow [Member]
Maximum [Member]
Dec. 31, 2012
Exelon Generation Co L L C [Member]
Derivative [Member]
Discounted Cash Flow [Member]
Dec. 31, 2012
Exelon Generation Co L L C [Member]
Derivative [Member]
Option Model Valuation Technique [Member]
Minimum [Member]
Dec. 31, 2012
Exelon Generation Co L L C [Member]
Derivative [Member]
Option Model Valuation Technique [Member]
Maximum [Member]
Dec. 31, 2012
Exelon Generation Co L L C [Member]
Proprietary Trading [Member]
Discounted Cash Flow [Member]
Dec. 31, 2012
Exelon Generation Co L L C [Member]
Proprietary Trading [Member]
Discounted Cash Flow [Member]
Minimum [Member]
Dec. 31, 2012
Exelon Generation Co L L C [Member]
Proprietary Trading [Member]
Discounted Cash Flow [Member]
Maximum [Member]
Dec. 31, 2012
Exelon Generation Co L L C [Member]
Proprietary Trading [Member]
Option Model Valuation Technique [Member]
Minimum [Member]
Dec. 31, 2012
Exelon Generation Co L L C [Member]
Proprietary Trading [Member]
Option Model Valuation Technique [Member]
Maximum [Member]
Dec. 31, 2013
Exelon Generation Co L L C [Member]
Fair Value Inputs Level 3 [Member]
Derivative [Member]
Dec. 31, 2013
Exelon Generation Co L L C [Member]
Fair Value Inputs Level 3 [Member]
Derivative [Member]
Discounted Cash Flow [Member]
Minimum [Member]
Dec. 31, 2013
Exelon Generation Co L L C [Member]
Fair Value Inputs Level 3 [Member]
Derivative [Member]
Discounted Cash Flow [Member]
Maximum [Member]
Dec. 31, 2013
Exelon Generation Co L L C [Member]
Fair Value Inputs Level 3 [Member]
Derivative [Member]
Option Model Valuation Technique [Member]
Minimum [Member]
Dec. 31, 2013
Exelon Generation Co L L C [Member]
Fair Value Inputs Level 3 [Member]
Derivative [Member]
Option Model Valuation Technique [Member]
Maximum [Member]
Dec. 31, 2013
Exelon Generation Co L L C [Member]
Fair Value Inputs Level 3 [Member]
Proprietary Trading [Member]
Dec. 31, 2013
Exelon Generation Co L L C [Member]
Fair Value Inputs Level 3 [Member]
Proprietary Trading [Member]
Discounted Cash Flow [Member]
Minimum [Member]
Dec. 31, 2013
Exelon Generation Co L L C [Member]
Fair Value Inputs Level 3 [Member]
Proprietary Trading [Member]
Discounted Cash Flow [Member]
Maximum [Member]
Dec. 31, 2013
Exelon Generation Co L L C [Member]
Fair Value Inputs Level 3 [Member]
Proprietary Trading [Member]
Option Model Valuation Technique [Member]
Minimum [Member]
Dec. 31, 2013
Exelon Generation Co L L C [Member]
Fair Value Inputs Level 3 [Member]
Proprietary Trading [Member]
Option Model Valuation Technique [Member]
Maximum [Member]
Dec. 31, 2012
Commonwealth Edison Co [Member]
Derivative [Member]
Discounted Cash Flow [Member]
Dec. 31, 2012
Commonwealth Edison Co [Member]
Derivative [Member]
Discounted Cash Flow [Member]
Minimum [Member]
Dec. 31, 2012
Commonwealth Edison Co [Member]
Derivative [Member]
Discounted Cash Flow [Member]
Maximum [Member]
Dec. 31, 2013
Commonwealth Edison Co [Member]
Fair Value Inputs Level 3 [Member]
Derivative [Member]
Dec. 31, 2013
Commonwealth Edison Co [Member]
Fair Value Inputs Level 3 [Member]
Derivative [Member]
Maximum [Member]
Dec. 31, 2013
Commonwealth Edison Co [Member]
Fair Value Inputs Level 3 [Member]
Derivative [Member]
Discounted Cash Flow [Member]
Minimum [Member]
Dec. 31, 2013
Commonwealth Edison Co [Member]
Fair Value Inputs Level 3 [Member]
Derivative [Member]
Discounted Cash Flow [Member]
Maximum [Member]
Derivatives Fair Value [Line Items]                                                            
Derivative Asset, Fair Value, Amount Not Offset Against Collateral $ 226,000,000         $ 473,000,000               $ 488,000,000                                
Derivative Liability, Fair Value, Amount Not Offset Against Collateral                 (6,000,000)                   3,000,000         (67,000,000)     (193,000,000)      
Fair Value Inputs [Abstract]                                                            
Forward power price assets       14 79                   8 176                            
Forward power price liabilities                   15 106                 10 176                  
Forward gas price assets       $ 3.26 $ 6.27                   $ 2.98 $ 16.63                            
Volatility percentage             28.00% 132.00%       16.00% 48.00%       15.00% 142.00%       14.00% 19.00%              
Marketability Reserve   8.00% 9.00%                                           3.50% 8.30%   8.00% 3.50%  
Forward heat rate   8.00% 9.50%                                                   8.00% 9.00%
Renewable factor                                                 81.00% 123.00%     84.00% 128.00%