Supplemental Financial Information - Taxes Other Than Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Supplemental Statement of Operations Information [Line Items]
Utility taxes	$ 196	$ 209	$ 414	$ 432
Property	149	148	297	296
Payroll	61	61	125	127
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	23	32	49	58
Property	64	68	133	138
Payroll	28	30	60	64
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	55	55	114	118
Property	8	9	15	15
Payroll	7	7	14	14
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	31	30	62	63
Property	4	4	8	8
Payroll	4	4	8	7
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	18	21	44	48
Property	40	37	79	75
Payroll	4	4	9	8
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	69	71	145	145
Property	33	30	62	60
Payroll	7	7	15	14
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	64	67	133	136
Property	21	21	41	43
Payroll	2	2	4	3
Delmarva Power and Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	5	4	10	9
Property	11	8	20	16
Payroll	1	1	2	2
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	0	0	1	0
Property	1	1	1	1
Payroll	$ 1	$ 1	$ 2	$ 2