Segment Information - Segment Financial Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,371	$ 1,330
Operating Expenses	1,229	1,157
Operating Income	142	173
Interest Expense	68	65
Other Income	9	13
Income Tax Expense (Benefit)	30	46
Net Income	53	75
Total Assets	16,027	15,004	15,667
Construction Expenditures	246	282
Operating Segments [Member] | Power Delivery [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,313	1,272
Operating Expenses	1,167	1,103
Operating Income	146	169
Interest Expense	58	55
Other Income	9	12
Income Tax Expense (Benefit)	35	47
Net Income	62	79
Total Assets	14,082	13,438
Construction Expenditures	241	264
Operating Segments [Member] | Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Operating Revenue	60	60
Operating Expenses	61	60
Operating Income	(1)
Income Tax Expense (Benefit)	(5)
Net Income	4
Total Assets	237	287
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(2)	(2)
Operating Expenses	1	(6)
Operating Income	(3)	4
Interest Expense	10	10
Other Income		1
Income Tax Expense (Benefit)		(1)
Net Income	(13)	(4)
Total Assets	1,708	1,279
Construction Expenditures	$ 5	$ 18