Supplemental Financial Information Supplemental Financial Information - Summary of Taxes other than income (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			$ 919	$ 898	$ 753
Property				557	545	483
Payroll				247	230	226
Other				60	58	114
Total taxes other than income				1,783	1,731	1,576
Exelon Generation Co L L C [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			114	126	122
Property				273	269	246
Payroll				130	121	117
Other				39	39	21
Total taxes other than income				556	555	506
Commonwealth Edison Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			243	240	242
Property				30	28	27
Payroll				27	26	28
Other				11	2	(4)
Total taxes other than income				311	296	293
PECO Energy Co [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			131	125	136
Property				15	14	13
Payroll				16	15	15
Other				1	0	0
Total taxes other than income				163	154	164
Baltimore Gas and Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			94	89	85
Property				143	132	123
Payroll				17	15	17
Other				0	4	4
Total taxes other than income				254	240	229
Pepco Holdings LLC [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			337	318
Property				94	101
Payroll				24	26
Other				0	7
Total taxes other than income				455	452
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]		$ 253
Property			73
Payroll			23
Other			5
Total taxes other than income			$ 354
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]	$ 78
Property		18
Payroll		8
Other		1
Total taxes other than income		$ 105
Potomac Electric Power Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			316	300	312
Property				58	62	53
Payroll				5	6	8
Other				0	3	4
Total taxes other than income				379	371	377
Delmarva Power & Light Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			21	18	18
Property				32	32	31
Payroll				3	4	5
Other				0	3	1
Total taxes other than income				56	57	55
Atlantic City Electric Company [Member]
Supplemental Statement of Operations Information [Line Items]
Utility	[1]			0	0	0
Property				3	3	3
Payroll				2	2	3
Other				0	1	1
Total taxes other than income				$ 5	$ 6	$ 7

[1] Generation’s utility tax represents gross receipts tax related to its retail operations and ComEd’s, PECO’s, BGE’s, Pepco's, DPL's and ACE's utility taxes represent municipal and state utility taxes and gross receipts taxes related to their operating revenues. The offsetting collection of utility taxes from customers is recorded in revenues in the Registrants’ Consolidated Statements of Operations and Comprehensive Income.