Debt and Credit Agreements - Issuance of Long-Term Debt (Details) $ in Millions	Jun. 30, 2020 USD ($)
Parent Company [Member] | Note405Apr2030 [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest Rate	4.05%
Debt Instrument, Face Amount	$ 1,250
Parent Company [Member] | Note470Apr2050 [Member] | Notes Payable to Banks [Member]
Debt Instrument [Line Items]
Interest Rate	4.70%
Debt Instrument, Face Amount	$ 750
Exelon Generation Co L L C [Member] | SN325June2025 [Member] | Energy Efficiency Project Financing [Member]
Debt Instrument [Line Items]
Interest Rate	3.25%
Debt Instrument, Face Amount	$ 900
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] | FMB220Mar2030 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	2.20%
Debt Instrument, Face Amount	$ 350
Commonwealth Edison Co [Member] | FMB300March2050 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	3.00%
Debt Instrument, Face Amount	$ 650
PECO Energy Co [Member] | FMB280June2050 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	2.80%
Debt Instrument, Face Amount	$ 350
Baltimore Gas and Electric Company [Member] | SN290June2050 [Member] | Energy Efficiency Project Financing [Member]
Debt Instrument [Line Items]
Interest Rate	2.90%
Debt Instrument, Face Amount	$ 400
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
Delmarva Power and Light Company [Member] | FMB253June2030 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	2.53%
Debt Instrument, Face Amount	$ 100
Delmarva Power and Light Company [Member] | Bonds105July2020 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	1.05%
Debt Instrument, Face Amount	$ 78
Atlantic City Electric Company [Member] | Bonds225June2029 [Member] | Tax-exempt Money Market Funds [Member]
Debt Instrument [Line Items]
Interest Rate	2.25%
Debt Instrument, Face Amount	$ 23
Atlantic City Electric Company [Member] | FMB324June2050 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Interest Rate	3.24%
Debt Instrument, Face Amount	$ 100