Regulatory Matters - Regulatory Assets COVID-19 (Details) $ in Millions	Sep. 30, 2020 USD ($)
Public Utilities, General Disclosures [Line Items]
COVID-19 Regulatory Asset	$ 60
Commonwealth Edison Co [Member]
Public Utilities, General Disclosures [Line Items]
COVID-19 Regulatory Asset	18
PECO Energy Co [Member]
Public Utilities, General Disclosures [Line Items]
COVID-19 Regulatory Asset	20
Baltimore Gas and Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
COVID-19 Regulatory Asset	11
Pepco Holdings LLC [Member]
Public Utilities, General Disclosures [Line Items]
COVID-19 Regulatory Asset	11
Potomac Electric Power Company [Member]
Public Utilities, General Disclosures [Line Items]
COVID-19 Regulatory Asset	8
Delmarva Power and Light Company [Member]
Public Utilities, General Disclosures [Line Items]
COVID-19 Regulatory Asset	3
Atlantic City Electric Company [Member]
Public Utilities, General Disclosures [Line Items]
COVID-19 Regulatory Asset	$ 0