Segment Information - Segment Financial Information for Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,344	$ 1,389	$ 3,575	$ 3,569
Operating Expenses	1,109	1,188	3,062	3,130
Operating Income	235	201	513	439
Interest Expense	68	66	205	190
Income Tax Expense (Benefit)	65	57	280	92
Total Assets (excluding Assets Held for Disposition	14,912		14,912		15,794
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,344	1,389	3,575	3,569
Operating Expenses	1,109	1,188	3,062	3,130
Operating Income	235	201	513	439
Interest Expense	68	66	205	190
Other Income (Loss)	8	9	24	27
Income Tax Expense (Benefit)	65	57	280	92
Net Income (Loss) from Continuing Operations	110	87	52	184
Total Assets (excluding Assets Held for Disposition	14,910	14,380	14,910	14,380
Construction Expenditures	327	299	943	888
Operating Segments [Member] | Power Delivery [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,298	1,335	3,428	3,374
Operating Expenses	1,067	1,136	2,934	2,950
Operating Income	231	199	494	424
Interest Expense	58	56	172	162
Other Income (Loss)	8	8	21	24
Income Tax Expense (Benefit)	67	59	115	93
Net Income (Loss) from Continuing Operations	114	92	228	193
Total Assets (excluding Assets Held for Disposition	12,790	12,039	12,790	12,039
Construction Expenditures	293	289	856	854
Operating Segments [Member] | Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Operating Revenue	48	57	154	205
Operating Expenses	50	64	151	209
Operating Income	(2)	(7)	3	(4)
Interest Expense	1	1	1	2
Other Income (Loss)	1	1	2	1
Income Tax Expense (Benefit)	(1)	(3)	1	(2)
Net Income (Loss) from Continuing Operations	(1)	(3)	3	(2)
Total Assets (excluding Assets Held for Disposition	341	426	341	426
Construction Expenditures	1	1	2	11
Interest Income		1		1
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(2)	(3)	(7)	(10)
Operating Expenses	(8)	(12)	(23)	(29)
Operating Income	6	9	16	19
Interest Expense	9	9	32	26
Other Income (Loss)	(1)		1	2
Income Tax Expense (Benefit)	(1)	1	164	1
Net Income (Loss) from Continuing Operations	(3)	(2)	(179)	(7)
Total Assets (excluding Assets Held for Disposition	1,779	1,915	1,779	1,915
Construction Expenditures	33	9	85	23
Interest Income		$ (1)		$ (1)