Supplemental Financial Information - Taxes Other Than Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Supplemental Statement of Operations Information [Line Items]
Utility taxes	$ 237	$ 241	$ 651	$ 672
Property	152	148	449	444
Payroll	59	57	183	185
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	26	29	75	87
Property	66	66	199	205
Payroll	29	28	88	92
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	66	66	181	183
Property	7	7	23	22
Payroll	7	7	21	21
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	41	38	102	102
Property	4	5	12	12
Payroll	4	3	12	11
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	21	21	65	68
Property	42	39	121	114
Payroll	4	4	13	13
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	83	86	228	231
Property	32	31	94	91
Payroll	6	6	21	20
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	77	81	210	217
Property	21	21	63	64
Payroll	2	2	6	5
Delmarva Power and Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	5	5	16	14
Property	10	9	29	25
Payroll	1	1	4	3
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	1	0	2	0
Property	1	0	2	2
Payroll	$ 1	$ 1	$ 3	$ 2