Supplemental Financial Information - Taxes Other Than Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Supplemental Statement of Operations Information [Line Items]
Utility taxes	$ 242	$ 237	$ 665	$ 651
Property	165	152	470	449
Payroll	57	59	180	183
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	27	26	73	75
Property	66	66	199	199
Payroll	26	29	83	88
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	67	66	188	181
Property	13	7	30	23
Payroll	7	7	20	21
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	41	41	107	102
Property	5	4	13	12
Payroll	4	4	12	12
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	21	21	66	65
Property	46	42	131	121
Payroll	5	4	14	13
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	86	83	231	228
Property	34	32	97	94
Payroll	7	6	21	21
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	80	77	212	210
Property	23	21	65	63
Payroll	2	2	5	6
Delmarva Power and Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	6	5	17	16
Property	10	10	30	29
Payroll	1	1	4	4
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	0	1	2	2
Property	1	1	2	2
Payroll	$ 1	$ 1	$ 2	$ 3