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Derivative Financial Instruments - Narrative (Details)
MWh in Millions, $ in Millions
1 Months Ended 9 Months Ended
Jun. 30, 2012
MWh
Sep. 30, 2021
USD ($)
Dec. 31, 2020
USD ($)
Derivative [Line Items]      
Incremental Collateral For Loss Of Investment Grade Credit Rating   $ 3,001 $ 1,432
Other   1,180 1,264
Exelon Generation Co L L C [Member]      
Derivative [Line Items]      
Incremental Collateral For Loss Of Investment Grade Credit Rating   3,001 1,432
Other   347 444
Commonwealth Edison Co [Member]      
Derivative [Line Items]      
Long-term Purchase Commitment, Minimum Energy Volume Required | MWh 1.3    
Other   165 143
PECO Energy Co [Member]      
Derivative [Line Items]      
Incremental Collateral For Loss Of Investment Grade Credit Rating   23  
Other   31 30
Baltimore Gas and Electric Company [Member]      
Derivative [Line Items]      
Incremental Collateral For Loss Of Investment Grade Credit Rating   46  
Other   81 91
Delmarva Power and Light Company [Member]      
Derivative [Line Items]      
Incremental Collateral For Loss Of Investment Grade Credit Rating   11  
Other   $ 41 20
Minimum [Member] | Exelon Generation Co L L C [Member]      
Derivative [Line Items]      
Expected Generation Hedged In Next Twelve Months   96.00%  
Maximum [Member] | Exelon Generation Co L L C [Member]      
Derivative [Line Items]      
Expected Generation Hedged In Next Twelve Months   99.00%  
Commodity Contract [Member] | Commonwealth Edison Co [Member] | External Counterparties | Collateral [Member]      
Derivative [Line Items]      
Other   $ 56  
Commodity Contract [Member] | Baltimore Gas and Electric Company [Member] | External Counterparties | Collateral [Member]      
Derivative [Line Items]      
Other   21  
Commodity Contract [Member] | Delmarva Power and Light Company [Member] | External Counterparties | Collateral [Member]      
Derivative [Line Items]      
Other   25  
Not Designated as Hedging Instrument, Economic Hedge [Member]      
Derivative [Line Items]      
Derivative, Notional Amount   567 665
Not Designated as Hedging Instrument, Economic Hedge [Member] | Exelon Generation Co L L C [Member]      
Derivative [Line Items]      
Derivative, Notional Amount   $ 567 $ 665