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, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			$ 898	$ 753	$ 474
Property				545	483	407
Payroll				230	226	201
Other				58	114	118
Total taxes other than income				1,731	1,576	1,200
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			126	122	105
Property				269	246	250
Payroll				121	117	118
Other				39	21	16
Total taxes other than income				555	506	489
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			240	242	236
Property				28	27	27
Payroll				26	28	28
Other				2	(4)	5
Total taxes other than income				296	293	296
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			125	136	133
Property				14	13	11
Payroll				15	15	14
Other				0	0	2
Total taxes other than income				154	164	160
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			89	85	85
Property				132	123	119
Payroll				15	17	16
Other				4	4	4
Total taxes other than income				240	229	224
Potomac Electric Power Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			300	312	308
Property				62	53	57
Payroll				6	8	6
Other				3	4	5
Total taxes other than income				371	377	376
Delmarva Power and Light Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			18	18	18
Property				32	31	28
Payroll				4	5	4
Other				3	1	1
Total taxes other than income				57	55	51
Atlantic City Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			0	0	0
Property				3	3	3
Payroll				2	3	2
Other				1	1	2
Total taxes other than income				6	$ 7	7
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]		$ 253	318
Property			73	101
Payroll			23	26
Other			5	7
Total taxes other than income			$ 354	$ 452
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]	$ 78				326
Property		18				94
Payroll		8				27
Other		1				8
Total taxes other than income		$ 105				$ 455

[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 on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.