Supplemental Financial Information - Utility Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Supplemental Statement of Operations Information [Line Items]
Utility taxes	$ 209	$ 218	$ 432	$ 452
Property	148	135	296	271
Payroll	61	65	127	133
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	32	29	58	60
Property	68	65	138	134
Payroll	30	34	64	68
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	55	60	118	121
Property	9	8	15	15
Payroll	7	7	14	14
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	30	30	63	63
Property	4	4	8	7
Payroll	4	4	7	8
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	21	21	48	47
Property	37	34	75	69
Payroll	4	4	8	8
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	71	78	145	161
Property	30	24	60	46
Payroll	7	6	14	14
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	67	73	136	151
Property	21	15	43	29
Payroll	2	2	3	3
Delmarva Power and Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	4	5	9	10
Property	8	8	16	16
Payroll	1	1	2	2
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	0	0	0	0
Property	1	1	1	1
Payroll	$ 1	$ 1	$ 2	$ 2