Segment Information - Segment Financial Information (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Goodwill	$ 1,406	$ 1,407	$ 1,406	$ 1,407	$ 1,407
Operating Revenue	1,140	1,117	2,511	2,447
Operating Expenses	1,001	966	2,230	2,123
Interest Expense	71	67	139	132
Interest and dividend income		1		1
Depreciation and amortization	157	132	316	265
Operating Segments [Member] | Power Delivery [Member]
Segment Reporting Information [Line Items]
Goodwill	1,400	1,400	1,400	1,400
Operating Revenue	1,078	1,040	2,391	2,312
Operating Expenses	940	881	2,107	1,984
Interest Expense	60	56	118	111
Depreciation and amortization	147	122	294	246
Operating Segments [Member] | Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Operating Revenue	63	79	123	139
Operating Expenses	62	77	123	137
Depreciation and amortization	0	2	1	4
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(1)	(2)	(3)	(4)
Operating Expenses	(1)	8		2
Interest Expense	11	11	21	21
Interest and dividend income		1		1
Depreciation and amortization	10	8	21	15
Corporate and Other [Member] | Inter Company Amounts [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(1)	(2)	(3)	(4)
Operating Expenses	(3)	(3)	(5)	(4)
Interest Expense	(1)	1	(2)
Interest and dividend income	$ (2)	$ (1)	$ (4)	$ (1)