Supplemental Financial Information - Summary of Taxes other than income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Statement of Operations Information [Line Items]
Utility	$ 881	$ 919	$ 898
Property	595	557	545
Payroll	232	247	230
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	112	114	126
Property	274	273	269
Payroll	115	130	121
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	242	243	240
Property	29	30	28
Payroll	27	27	26
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	132	131	125
Property	17	15	14
Payroll	15	16	15
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	90	94	89
Property	153	143	132
Payroll	17	17	15
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	304	337	318
Property	122	94	101
Payroll	24	24	26
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	286	316	300
Property	85	58	62
Payroll	7	5	6
Delmarva Power & Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	18	21	18
Property	34	32	32
Payroll	4	3	4
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	0	0	0
Property	2	3	3
Payroll	$ 2	$ 2	$ 2