Supplemental Financial Information - Summary of Taxes other than income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental Statement of Operations Information [Line Items]
Utility	$ 859	$ 881	$ 919
Property	602	595	557
Payroll	235	232	247
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	99	112	114
Property	265	274	273
Payroll	113	115	130
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	238	242	243
Property	30	29	30
Payroll	27	27	27
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	135	132	131
Property	16	17	15
Payroll	16	15	16
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	87	90	94
Property	164	153	143
Payroll	17	17	17
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	299	304	337
Property	126	122	94
Payroll	25	24	24
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	275	286	316
Property	84	85	58
Payroll	7	7	5
Delmarva Power & Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	21	18	21
Property	39	34	32
Payroll	5	4	3
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	3	0	0
Property	3	2	3
Payroll	$ 3	$ 2	$ 2