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, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			$ 753	$ 474	$ 456
Property				483	407	396
Payroll				226	201	200
Other				114	118	102
Total taxes other than income				1,576	1,200	1,154
Exelon Generation Co L L C [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			122	105	89
Property				246	250	240
Payroll				117	118	118
Other				21	16	18
Total taxes other than income				506	489	465
Commonwealth Edison Co [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			242	236	238
Property				27	27	25
Payroll				28	28	28
Other				(4)	5	2
Total taxes other than income				293	296	293
PECO Energy Co [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			136	133	128
Property				13	11	15
Payroll				15	14	14
Other				0	2	2
Total taxes other than income				164	160	159
Baltimore Gas and Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			85	85	86
Property				123	119	114
Payroll				17	16	18
Other				4	4	3
Total taxes other than income				229	224	221
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]		$ 253
Property			73
Payroll			23
Other			5
Total taxes other than income			$ 354
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]	$ 78			326	324
Property		18			94	85
Payroll		8			27	23
Other		1			8	5
Total taxes other than income		$ 105			455	437
Potomac Electric Power Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			312	308	307
Property				53	57	51
Payroll				8	6	6
Other				4	5	5
Total taxes other than income				377	376	369
Delmarva Power and Light Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			18	18	17
Property				31	28	24
Payroll				5	4	4
Other				1	1	1
Total taxes other than income				55	51	46
Atlantic City Electric Company [Member]
Supplemental Financial Information Tables [Line Items]
Utilities Operating Expense, Taxes	[1]			0	0	0
Property				3	3	3
Payroll				3	2	2
Other				1	2	(1)
Total taxes other than income				$ 7	$ 7	$ 4

[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.