Debt and Credit Agreements - Issuance of Long-Term Debt (Details) $ in Millions	Sep. 30, 2018 USD ($)
Exelon Generation Co L L C [Member] | EEPF372Nov2018 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	3.72%
Debt Instrument, Face Amount	$ 4
Exelon Generation Co L L C [Member] | EEPF317Oct2018 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	3.17%
Debt Instrument, Face Amount	$ 1
Exelon Generation Co L L C [Member] | EEPF261Sep2018 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	2.61%
Debt Instrument, Face Amount	$ 5
Exelon Generation Co L L C [Member] | EEPF417Jan2019 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	4.17%
Debt Instrument, Face Amount	$ 1
Exelon Generation Co L L C [Member] | EEPF426May2019 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	4.26%
Debt Instrument, Face Amount	$ 3
Commonwealth Edison Co [Member] | FMB400Mar2048Member | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	4.00%
Debt Instrument, Face Amount	$ 800
Commonwealth Edison Co [Member] | FMB370Aug2028 [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	3.70%
Debt Instrument, Face Amount	$ 550
PECO Energy Co [Member] | FRMB390Mar2048 [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	3.90%
Debt Instrument, Face Amount	$ 325
PECO Energy Co [Member] | PIDC200Jun2023 [Member] | Long-term Debt [Member]
Debt Instrument [Line Items]
Interest Rate	2.00%
Debt Instrument, Face Amount	$ 50
PECO Energy Co [Member] | FRMB390Mar2048B [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	3.90%
Debt Instrument, Face Amount	$ 325
Baltimore Gas and Electric Company [Member] | SN425Sep2048 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Interest Rate	4.25%
Debt Instrument, Face Amount	$ 300
Potomac Electric Power Company [Member] | FMB427Jun2048 [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	4.27%
Debt Instrument, Face Amount	$ 100
Delmarva Power and Light Company [Member] | FMB427Jun2048 [Member] | First Mortgage [Member]
Debt Instrument [Line Items]
Interest Rate	4.27%
Debt Instrument, Face Amount	$ 200