Supplemental Financial Information - Taxes Other Than Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Supplemental Statement of Operations Information [Line Items]
Utility taxes	$ 218	$ 223
Property	150	149
Payroll	63	65
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	26	26
Property	69	71
Payroll	31	33
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	60	62
Property	7	7
Payroll	7	7
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	31	34
Property	4	3
Payroll	4	4
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	26	27
Property	39	37
Payroll	4	4
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	75	74
Property	31	29
Payroll	8	7
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	69	69
Property	21	21
Payroll	2	2
Delmarva Power and Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	6	5
Property	9	8
Payroll	1	1
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility taxes	0	0
Property	1	0
Payroll	$ 1	$ 1