Debt and Credit Agreements - Issuance of Long-Term Debt (Details) $ in Millions	Sep. 30, 2019 USD ($)
Exelon Generation Co L L C [Member] | EEPF395Aug2020 [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Interest Rate	3.95%
Debt Instrument, Face Amount	$ 4
Exelon Generation Co L L C [Member] | EEPF346May2020 [Member] | Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Interest Rate	3.46%
Debt Instrument, Face Amount	$ 39
Commonwealth Edison Co [Member] | FMB400Mar2049 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	4.00%
Debt Instrument, Face Amount	$ 400
PECO Energy Co [Member] | FRMB300Sep2049 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	3.00%
Debt Instrument, Face Amount	$ 325
Baltimore Gas and Electric Company [Member] | SN320Sep2049 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest Rate	3.20%
Debt Instrument, Face Amount	$ 400
Potomac Electric Power Company [Member] | FMB345Jun2029 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	3.45%
Debt Instrument, Face Amount	$ 150
Potomac Electric Power Company [Member] | Medco170Sep2022 [Member] | Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Interest Rate	1.70%
Debt Instrument, Face Amount	$ 110
Atlantic City Electric Company [Member] | FMB350May2029 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	3.50%
Debt Instrument, Face Amount	$ 100
Atlantic City Electric Company [Member] | FMB414May2049 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	4.14%
Debt Instrument, Face Amount	$ 50