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Regulatory Matters - Annual Electric Transmission Fillings (Details) - USD ($)
$ in Millions
Jul. 17, 2020
May 29, 2020
May 15, 2020
2020 Transmission Formula Rate Revenue Reduction [Member] | Baltimore Gas and Electric Company [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount     $ 9
2020 Transmission Formula Rate Annual Update [Domain] | Commonwealth Edison Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Requested Rate Increase (Decrease), Amount     18
Revenue     (4)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount     $ 14
Public Utilities, Approved Equity Capital Structure, Percentage     8.17%
Public Utilities, Approved Return on Equity, Percentage     11.50%
Cap on Equity Component of Rate of Return on Common Equity in Federal Energy Regulatory Committee Complaint     55.00%
2020 Transmission Formula Rate Annual Update [Domain] | PECO Energy Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Approved Equity Capital Structure, Percentage   7.47%  
Public Utilities, Approved Return on Equity, Percentage   10.35%  
Cap on Equity Component of Rate of Return on Common Equity in Federal Energy Regulatory Committee Complaint   55.75%  
2020 Transmission Formula Rate Annual Update [Domain] | Baltimore Gas and Electric Company [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Requested Rate Increase (Decrease), Amount     $ 16
Revenue     (3)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount     $ 4
Public Utilities, Approved Equity Capital Structure, Percentage     7.26%
Public Utilities, Approved Return on Equity, Percentage     10.50%
2020 Transmission Formula Rate Annual Update [Domain] | Potomac Electric Power Company [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Requested Rate Increase (Decrease), Amount     $ 2
Revenue     (46)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount     $ (44)
Public Utilities, Approved Equity Capital Structure, Percentage     7.81%
Public Utilities, Approved Return on Equity, Percentage     10.50%
2020 Transmission Formula Rate Annual Update [Domain] | Delmarva Power and Light Company [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Requested Rate Increase (Decrease), Amount     $ (4)
Revenue     (40)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount     $ (44)
Public Utilities, Approved Equity Capital Structure, Percentage     7.20%
Public Utilities, Approved Return on Equity, Percentage     10.50%
2020 Transmission Formula Rate Annual Update [Domain] | Atlantic City Electric Company [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Requested Rate Increase (Decrease), Amount     $ 5
Revenue     (25)
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount     $ (20)
Public Utilities, Approved Equity Capital Structure, Percentage     7.40%
Public Utilities, Approved Return on Equity, Percentage     10.50%
Subsequent Event [Member] | 2020 Transmission Formula Rate Annual Update [Domain] | PECO Energy Co [Member]      
Public Utilities, General Disclosures [Line Items]      
Public Utilities, Requested Rate Increase (Decrease), Amount $ 5    
Revenue (28)    
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount $ (23)