Debt and Credit Agreements - Issuance of Long-Term Debt (Details) $ in Millions	Mar. 31, 2020 USD ($)
Exelon Generation Co L L C [Member] | EEPF395Aug2020 [Member] | Energy Efficiency Project Financing [Member]
Debt Instrument [Line Items]
Interest Rate	3.95%
Debt Instrument, Face Amount	$ 2
Exelon Generation Co L L C [Member] | EEPF253April2021 [Member] | Energy Efficiency Project Financing [Member]
Debt Instrument [Line Items]
Interest Rate	2.53%
Debt Instrument, Face Amount	$ 1
Commonwealth Edison Co [Member] | FMB300March2050 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	3.00%
Debt Instrument, Face Amount	$ 650
Commonwealth Edison Co [Member] | FMB220Mar2030 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	2.20%
Debt Instrument, Face Amount	$ 350
Potomac Electric Power Company [Member] | FMB253Feb2030 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	2.53%
Debt Instrument, Face Amount	$ 150
Potomac Electric Power Company [Member] | FMB328Sep2050 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	3.28%
Debt Instrument, Face Amount	$ 150