Segment Information - Segment Financial Information for Continuing Operations (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		0 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Corporate and Other [Member]	Sep. 30, 2013 Corporate and Other [Member]	Sep. 30, 2014 Corporate and Other [Member]	Sep. 30, 2013 Corporate and Other [Member]	Sep. 30, 2014 Pepco Energy Services [Member]	Sep. 30, 2014 Pepco Energy Services [Member]	Sep. 30, 2014 Pepco Energy Services [Member]	Sep. 30, 2014 Operating Segments [Member] Power Delivery [Member]	Sep. 30, 2013 Operating Segments [Member] Power Delivery [Member]	Sep. 30, 2014 Operating Segments [Member] Power Delivery [Member]	Sep. 30, 2013 Operating Segments [Member] Power Delivery [Member]	Sep. 30, 2014 Operating Segments [Member] Pepco Energy Services [Member]	Sep. 30, 2013 Operating Segments [Member] Pepco Energy Services [Member]	Sep. 30, 2014 Operating Segments [Member] Pepco Energy Services [Member]	Sep. 30, 2013 Operating Segments [Member] Pepco Energy Services [Member]	Sep. 30, 2014 Intersegment [Member] Corporate and Other [Member]	Sep. 30, 2013 Intersegment [Member] Corporate and Other [Member]	Sep. 30, 2014 Intersegment [Member] Corporate and Other [Member]	Sep. 30, 2013 Intersegment [Member] Corporate and Other [Member]
Segment Reporting Information [Line Items]
Goodwill	$ 1,407		$ 1,407		$ 1,407								$ 1,400	$ 1,400	$ 1,400	$ 1,400
Operating Revenue	1,313	1,344	3,760	3,575		(2)	(2)	(6)	(7)				1,242	1,298	3,554	3,428	73	48	212	154	(2)	(2)	(6)	(8)
Operating Expenses	1,147	1,109	3,270	3,062			(8)	2	(23)				1,021	1,067	3,005	2,934	126	50	263	151	(1)	(1)	(5)	(7)
Interest Expense	68	68	200	205		9	9	30	32				58	58	169	172	1	1	1	1	(2)	(2)	(2)	(6)
Interest Income																					(2)	(2)	(3)	(7)
Depreciation and amortization	145	124	410	352									135	116	381	327	2		6	4	8	8	23	21
Impairment loss	53		53							53	53	53
Impairment loss, after-tax										32	32	32
Interest benefit on uncertain tax positions																12
Interest expense on uncertain tax positions																								66
Valuation allowances against deferred tax assets																								$ 101