Segment Information - Segment Financial Information for Continuing Operations (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting Information [Line Items]
Goodwill	$ 1,407				$ 1,407				$ 1,407	$ 1,407
Operating Revenue	1,091	1,344	1,051	1,180	1,056	1,389	1,057	1,123	4,666	4,625	4,964
Operating Expenses	(936)	(1,109)	(906)	(1,047)	(954)	(1,188)	(932)	(1,010)	(3,998)	(4,084)	(4,411)
Interest expense									(273)	(256)	(242)
Depreciation and amortization									473	454	425
Impairment losses, pre-tax									4	12
Tax benefits									(128)	(166)	(72)
Power Delivery [Member]
Segment Reporting Information [Line Items]
Goodwill	1,400				1,400				1,400	1,400	1,400
Depreciation and amortization									439	416	394
Interest benefit									12
Tax benefits											14
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									28	24	15
Interest expense on uncertain tax positions									66
Corporate and Other [Member] | Intersegment [Member]
Segment Reporting Information [Line Items]
Operating Revenue									(10)	(11)	(16)
Operating Expenses									(9)	(10)	(15)
Interest expense									(5)	(18)	(22)
Interest Income										(21)	(22)
Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									6	14	16
Impairment losses, pre-tax									4	12
Impairment losses, after-tax									3	7
Other Non-Regulated [Member]
Segment Reporting Information [Line Items]
Valuation allowance against deferred tax assets									101
Retail Electric and Natural Gas Supply Businesses of Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Operating Revenue										$ 9	$ 15