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Nuclear Decommissioning - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
Jun. 30, 2021
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Nuclear decommissioning trust funds $ 15,404   $ 15,404   $ 14,464
Increase in PPE related to ARO update     574 $ 775  
Nuclear Decommissioning [Member]          
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Net increase (decrease) due to changes in, and timing of, estimated future cash flows     256    
Increase (Decrease) in ARO Due to Reversal of Early Retirement     (170)    
Increase (Decrease) in ARO for Impacts of Revised Decommissioning Cost Estimates     (110)    
Increase (Decrease) in ARO Due to Updated Cost Escalation Rates and Discount Rates     510    
Nuclear Decommissioning [Member] | Operating Expense [Member]          
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Asset Retirement Obligation, Revision of Estimate     (51)    
Nuclear Decommissioning Byron          
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Decommissioning Related Activities Not Contractually Offset 140 $ 53      
Exelon Generation Co L L C [Member]          
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Nuclear decommissioning trust funds 15,404   15,404   14,464
Increase in PPE related to ARO update     550 $ 775  
Exelon Generation Co L L C [Member] | Nuclear Decommissioning [Member]          
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Net increase (decrease) due to changes in, and timing of, estimated future cash flows     256    
Increase (Decrease) in ARO Due to Reversal of Early Retirement     (170)    
Increase (Decrease) in ARO for Impacts of Revised Decommissioning Cost Estimates     (110)    
Increase (Decrease) in ARO Due to Updated Cost Escalation Rates and Discount Rates     510    
Exelon Generation Co L L C [Member] | Nuclear Decommissioning [Member] | Operating Expense [Member]          
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Asset Retirement Obligation, Revision of Estimate     (51)    
Exelon Generation Co L L C [Member] | Nuclear Decommissioning Byron          
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Decommissioning Related Activities Not Contractually Offset 140 $ 53      
Assets, Total [Member]          
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Nuclear decommissioning trust funds 15,602   15,602   14,599
Assets, Total [Member] | Exelon Generation Co L L C [Member]          
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Nuclear decommissioning trust funds 15,602   15,602   14,599
Other Current Assets [Member]          
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Nuclear decommissioning trust funds 198   198   134
Other Current Assets [Member] | Exelon Generation Co L L C [Member]          
Nuclear Decommissioning Additional Narrative Information [Line Items]          
Nuclear decommissioning trust funds $ 198   $ 198   $ 134