Segment Information - Segment Financial Information for Continuing Operations (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Goodwill	$ 1,407		$ 1,407		$ 1,407
Operating Revenue	1,053	1,070	1,865	2,206
Operating Expenses	(921)	(933)	(1,969)	(1,943)
Depreciation and amortization	116	111	228	221
Interest Expense	70	65	137	130
Impairment losses		3		3
Interest expense on uncertain tax positions			16
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	6	7	12	11
Power Delivery [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	107	100	211	199
Interest benefit			12
Power Delivery [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Goodwill	1,400	1,400	1,400	1,400
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	(5)	(4)	(6)	(8)
Operating Expenses	(5)	(1)	(6)	(7)
Interest Income	(2)	(6)	(5)	(11)
Interest Expense		(5)	(4)	(10)
Preferred Stock Dividends			(1)	(1)
Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	2	4	4	10
Impairment losses		3		3
Other Non-Regulated [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	1		1	1
Non-cash pre-tax charge			373
Interest expense on uncertain tax positions			16
Non cash charges for tax consequences			64
Valuation allowance against deferred tax assets			$ 101