Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Other, Net [Abstract]
AFUDC - Equity	$ 36	$ 28
Non-service net periodic benefit cost	17	20
Commonwealth Edison Co [Member]
Other, Net [Abstract]
AFUDC - Equity	8	4
Non-service net periodic benefit cost	0	0
PECO Energy Co [Member]
Other, Net [Abstract]
AFUDC - Equity	7	6
Non-service net periodic benefit cost	0	0
Baltimore Gas and Electric Company [Member]
Other, Net [Abstract]
AFUDC - Equity	6	7
Non-service net periodic benefit cost	0	0
Pepco Holdings LLC [Member]
Other, Net [Abstract]
AFUDC - Equity	15	11
Non-service net periodic benefit cost	0	0
Potomac Electric Power Company [Member]
Other, Net [Abstract]
AFUDC - Equity	11	9
Non-service net periodic benefit cost	0	0
Delmarva Power and Light Company [Member]
Other, Net [Abstract]
AFUDC - Equity	2	1
Non-service net periodic benefit cost	0	0
Atlantic City Electric Company [Member]
Other, Net [Abstract]
AFUDC - Equity	2	1
Non-service net periodic benefit cost	$ 0	$ 0