Supplemental Financial Information - Taxes Other Than Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Supplemental Statement of Operations Information [Line Items]
Utility taxes	$ 206	$ 196	$ 423	$ 414
Property	153	149	307	297
Payroll	61	61	122	125
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	22	23	46	49
Property	66	64	133	133
Payroll	30	28	58	60
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	61	55	121	114
Property	8	8	16	15
Payroll	6	7	13	14
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	32	31	66	62
Property	4	4	9	8
Payroll	4	4	8	8
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	20	18	45	44
Property	43	40	85	79
Payroll	5	4	9	9
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	71	69	145	145
Property	31	33	63	62
Payroll	7	7	14	15
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	65	64	132	133
Property	20	21	42	41
Payroll	1	2	3	4
Delmarva Power and Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	5	5	11	10
Property	10	11	19	20
Payroll	1	1	3	2
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	0	0	1	1
Property	1	1	1	1
Payroll	$ 1	$ 1	$ 2	$ 2