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Income Taxes - Narrative (Details) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended 6 Months Ended
Sep. 30, 2014
Jun. 30, 2016
Jun. 30, 2015
Mar. 31, 2014
Jun. 30, 2016
Dec. 31, 2015
Dec. 31, 2009
Income Tax Additional Narrative Information [Line Items]              
Unrecognized Tax Benefits   $ (963)     $ (963) $ (1,101)  
Unrecognized Tax Benefits, Period Increase (Decrease)   328     190    
Unrecognized tax benefits that if recognized would affect the effective tax rate   75     75    
Increase (Decrease) in Income Taxes         300    
Deferred tax gain under involuntary conversion provisions of the IRC             $ 1,200
IRS asserted penalties for understatement of tax         90    
Expected non-cash charge to earnings       $ 265      
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position   460     460    
Early termination amount     $ 335        
Taxes Payable, Current     360        
Tax Adjustments, Settlements, and Unusual Provisions         310    
Parent Company [Member]              
Income Tax Additional Narrative Information [Line Items]              
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities         1    
Exelon Generation Co L L C [Member]              
Income Tax Additional Narrative Information [Line Items]              
Unrecognized Tax Benefits   (531)     (531) (534)  
Increase (Decrease) in Income Taxes $ 67            
Effective Income Tax Rate Reconciliation, Tax Settlement, Amount   120          
Tax Adjustments, Settlements, and Unusual Provisions         6    
Commonwealth Edison Co [Member]              
Income Tax Additional Narrative Information [Line Items]              
Unrecognized Tax Benefits   12     12 (142)  
Unrecognized Tax Benefits, Period Increase (Decrease)   154          
Unrecognized tax benefits that if recognized would affect the effective tax rate   12     12    
Expected non-cash charge to earnings       172      
Non-cash equity contributions       $ 172      
Potential tax and interest from a successful IRS challenge of the like-kind exchange transaction position   275     275    
Taxes Payable, Current     $ 65        
Tax Adjustments, Settlements, and Unusual Provisions         12    
PECO Energy Co [Member]              
Income Tax Additional Narrative Information [Line Items]              
Unrecognized Tax Benefits   0     0 0  
Baltimore Gas and Electric Company [Member]              
Income Tax Additional Narrative Information [Line Items]              
Unrecognized Tax Benefits   (120)     (120) (120)  
Pepco Holdings LLC [Member]              
Income Tax Additional Narrative Information [Line Items]              
Unrecognized Tax Benefits   (181)     (181)    
Unrecognized Tax Benefits, Period Increase (Decrease)   159          
PEPCO Holdings Inc [Member]              
Income Tax Additional Narrative Information [Line Items]              
Fresh-Start Adjustment, Increase (Decrease), Deferred Income Tax Liabilities, Noncurrent   8     8    
Potomac Electric Power Company [Member]              
Income Tax Additional Narrative Information [Line Items]              
Unrecognized Tax Benefits   (95)     (95) (8)  
Unrecognized Tax Benefits, Period Increase (Decrease)   87          
Increase (Decrease) in Income Taxes 71            
Delmarva Power and Light Company [Member]              
Income Tax Additional Narrative Information [Line Items]              
Unrecognized Tax Benefits   (39)     (39) (3)  
Unrecognized Tax Benefits, Period Increase (Decrease)   36          
Increase (Decrease) in Income Taxes $ 20            
Atlantic City Electric Company [Member]              
Income Tax Additional Narrative Information [Line Items]              
Unrecognized Tax Benefits   (24)     $ (24) $ 0  
Unrecognized Tax Benefits, Period Increase (Decrease)   $ 24