Segment Information - Segment Financial Information for Continuing Operations (Parenthetical) (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]
Goodwill	$ 1,407		$ 1,407		$ 1,407
Operating Revenue	1,344	1,389	3,575	3,569
Operating Expenses	(1,109)	(1,188)	(3,062)	(3,130)
Interest Expense	(68)	(66)	(205)	(190)
Depreciation and amortization	124	122	352	343
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	8	6	21	18
Power Delivery [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	116	114	327	313
Interest benefit			12
Power Delivery [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Goodwill	1,400	1,400	1,400	1,400
Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		2	4	12
Impairment losses, pre-tax		2		5
Impairment losses, after-tax		1		3
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Interest expense on uncertain tax positions			66
Corporate and Other [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(2)	(3)	(8)	(11)
Operating Expenses	(1)	(4)	(7)	(11)
Interest Income	(2)	(7)	(7)	(18)
Interest Expense	(2)	(5)	(6)	(15)
Other Non-Regulated [Member]
Segment Reporting Information [Line Items]
Valuation allowance against deferred tax assets			$ 101