Income Taxes - Allocation of Tax Benefits (Details) - USD ($) $ in Millions	Sep. 30, 2022	Sep. 30, 2021
Commonwealth Edison Co [Member]
Allocation of Tax Benefits [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	$ 1	$ 1
PECO Energy Co [Member]
Allocation of Tax Benefits [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	47	19
Baltimore Gas and Electric Company [Member]
Allocation of Tax Benefits [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	0	0
Pepco Holdings LLC [Member]
Allocation of Tax Benefits [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	28	17
Potomac Electric Power Company [Member]
Allocation of Tax Benefits [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	23	16
Delmarva Power and Light Company [Member]
Allocation of Tax Benefits [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	3	0
Atlantic City Electric Company [Member]
Allocation of Tax Benefits [Line Items]
Allocation Of Federal Tax Benefit Under Tax Sharing Agreement	$ 2	$ 0