Commitments and Contingencies - Schedule of Accruals for Environmental Matters (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	$ 474	$ 483
Exelon Generation Co L L C [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	119	121
Commonwealth Edison Co [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	284	293
PECO Energy Co [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	23	23
Baltimore Gas and Electric Company [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	6	2
Pepco Holdings LLC [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	42	44
Potomac Electric Power Company [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	40	42
Delmarva Power and Light Company [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	1	1
Atlantic City Electric Company [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	1	1
Manufactured Gas Plants [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	310	314
Manufactured Gas Plants [Member] | Exelon Generation Co L L C [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	0	0
Manufactured Gas Plants [Member] | Commonwealth Edison Co [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	284	293
Manufactured Gas Plants [Member] | PECO Energy Co [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	21	21
Manufactured Gas Plants [Member] | Baltimore Gas and Electric Company [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	5	0
Manufactured Gas Plants [Member] | Pepco Holdings LLC [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	0	0
Manufactured Gas Plants [Member] | Potomac Electric Power Company [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	0	0
Manufactured Gas Plants [Member] | Delmarva Power and Light Company [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	0	0
Manufactured Gas Plants [Member] | Atlantic City Electric Company [Member]
Site Contingency [Line Items]
Total environmental investigation and remediation reserve	$ 0	$ 0