Supplemental Financial Information - Utility Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Supplemental Statement of Operations Information [Line Items]
Utility taxes	$ 241	$ 253	$ 672	$ 705
Property	148	145	444	416
Payroll	57	58	185	191
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	29	32	87	92
Property	66	70	205	204
Payroll	28	31	92	99
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	66	67	183	188
Property	7	7	22	22
Payroll	7	6	21	20
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	38	39	102	102
Property	5	4	12	12
Payroll	3	3	11	11
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	21	23	68	70
Property	39	37	114	106
Payroll	4	4	13	12
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	86	92	231	253
Property	31	26	91	71
Payroll	6	5	20	19
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	81	87	217	238
Property	21	16	64	45
Payroll	2	1	5	5
Delmarva Power and Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	5	5	14	15
Property	9	9	25	24
Payroll	1	1	3	3
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	0	0	0	0
Property	0	0	2	2
Payroll	$ 1	$ 1	$ 2	$ 2