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Nuclear Decommissioning - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Mar. 31, 2019
Jun. 30, 2019
Dec. 31, 2018
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Asset Retirement Obligation, Period Increase (Decrease)   $ 432  
Asset Retirement Obligation, Revision of Estimate $ 330    
Decommissioning Fund Investments   12,513 $ 11,661
Assets held for sale   880 904
Exelon Generation Co L L C [Member]      
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Asset Retirement Obligation, Period Increase (Decrease)   432  
Asset Retirement Obligation, Revision of Estimate 330    
Decommissioning Fund Investments   12,513 11,661
Assets held for sale   880 904
Nuclear Decommissioning [Member]      
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Asset Retirement Obligation, Revision of Estimate   232  
Nuclear Decommissioning [Member] | Exelon Generation Co L L C [Member]      
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Asset Retirement Obligation, Revision of Estimate   232  
Three Mile Island [Member]      
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Asset Retirement Obligation, Period Increase (Decrease) (110)    
Asset Retirement Obligation Revision Of Estimate In Operating And Maintenance Expense (85)    
Three Mile Island [Member] | Exelon Generation Co L L C [Member]      
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Asset Retirement Obligation, Period Increase (Decrease) (110)    
Asset Retirement Obligation Revision Of Estimate In Operating And Maintenance Expense $ (85)    
Assets, Total [Member]      
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Decommissioning Fund Investments   13,498 12,695
Assets, Total [Member] | Exelon Generation Co L L C [Member]      
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Decommissioning Fund Investments   13,498 12,695
Nuclear Decommissioning Trust Fund Investments [Member] | Oyster Creek [Member]      
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Assets held for sale   857 890
Nuclear Decommissioning Trust Fund Investments [Member] | Oyster Creek [Member] | Exelon Generation Co L L C [Member]      
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Assets held for sale   857 890
Other Current Assets [Member]      
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Decommissioning Fund Investments   127 144
Other Current Assets [Member] | Exelon Generation Co L L C [Member]      
Nuclear Decommissioning Additional Narrative Information [Line Items]      
Decommissioning Fund Investments   $ 127 $ 144