Supplemental Financial Information - Operations (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Other, Net [Abstract]
AFUDC - Equity	$ 38	$ 34	$ 74	$ 64
Non-service net periodic benefit cost	16	26	33	46
Commonwealth Edison Co [Member]
Other, Net [Abstract]
AFUDC - Equity	9	9	17	13
Non-service net periodic benefit cost	0	0	0	0
PECO Energy Co [Member]
Other, Net [Abstract]
AFUDC - Equity	8	6	15	12
Non-service net periodic benefit cost	0	0	0	0
Baltimore Gas and Electric Company [Member]
Other, Net [Abstract]
AFUDC - Equity	6	7	12	14
Non-service net periodic benefit cost	0	0	0	0
Pepco Holdings LLC [Member]
Other, Net [Abstract]
AFUDC - Equity	15	12	30	25
Non-service net periodic benefit cost	0	0	0	0
Potomac Electric Power Company [Member]
Other, Net [Abstract]
AFUDC - Equity	11	10	22	20
Non-service net periodic benefit cost	0	0	0	0
Delmarva Power and Light Company [Member]
Other, Net [Abstract]
AFUDC - Equity	2	1	4	3
Non-service net periodic benefit cost	0	0	0	0
Atlantic City Electric Company [Member]
Other, Net [Abstract]
AFUDC - Equity	2	1	4	2
Non-service net periodic benefit cost	$ 0	$ 0	$ 0	$ 0