Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Other, Net [Abstract]
AFUDC - Equity	$ 38	$ 36	$ 112	$ 99
Non-service net periodic benefit cost	16	19	48	64
Commonwealth Edison Co [Member]
Other, Net [Abstract]
AFUDC - Equity	10	10	28	23
Non-service net periodic benefit cost	0	0	0	0
PECO Energy Co [Member]
Other, Net [Abstract]
AFUDC - Equity	7	7	22	19
Non-service net periodic benefit cost	0	0	0	0
Baltimore Gas and Electric Company [Member]
Other, Net [Abstract]
AFUDC - Equity	5	7	17	21
Non-service net periodic benefit cost	0	0	0	0
Pepco Holdings LLC [Member]
Other, Net [Abstract]
AFUDC - Equity	16	12	45	36
Non-service net periodic benefit cost	0	0	0	0
Potomac Electric Power Company [Member]
Other, Net [Abstract]
AFUDC - Equity	12	9	35	30
Non-service net periodic benefit cost	0	0	0	0
Delmarva Power and Light Company [Member]
Other, Net [Abstract]
AFUDC - Equity	2	2	5	4
Non-service net periodic benefit cost	0	0	0	0
Atlantic City Electric Company [Member]
Other, Net [Abstract]
AFUDC - Equity	2	1	5	2
Non-service net periodic benefit cost	$ 0	$ 0	$ 0	$ 0