Segment Information - Segment Financial Information (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,140		$ 1,117	$ 2,511	$ 2,447
Operating Expenses	1,001		966	2,230	2,123
Operating Income	139		151	281	324
Interest Expense	71		67	139	132
Interest and dividend income			1		1
Other Income (Expense)	12		13	21	26
Income Tax Expense (Benefit)	27		45	57	91
Net Income	53	$ 53	53	106	128
Total Assets	16,132		15,070	16,132	15,070	$ 15,667
Construction Expenditures	316		271	562	553
Operating Segments [Member] | Power Delivery [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,078		1,040	2,391	2,312
Operating Expenses	940		881	2,107	1,984
Operating Income	138		159	284	328
Interest Expense	60		56	118	111
Other Income (Expense)	12		13	21	25
Income Tax Expense (Benefit)	29		45	64	92
Net Income	61		71	123	150
Total Assets	14,184		13,471	14,184	13,471
Construction Expenditures	305		253	546	517
Operating Segments [Member] | Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Operating Revenue	63		79	123	139
Operating Expenses	62		77	123	137
Operating Income	1		2		2
Other Income (Expense)			1		1
Income Tax Expense (Benefit)			1	(5)	1
Net Income	1		2	5	2
Total Assets	233		297	233	297
Construction Expenditures	2		1	2	1
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(1)		(2)	(3)	(4)
Operating Expenses	(1)		8		2
Operating Income			(10)	(3)	(6)
Interest Expense	11		11	21	21
Interest and dividend income			1		1
Other Income (Expense)			(1)
Income Tax Expense (Benefit)	(2)		(1)	(2)	(2)
Net Income	(9)		(20)	(22)	(24)
Total Assets	1,715		1,302	1,715	1,302
Construction Expenditures	$ 9		$ 17	$ 14	$ 35