Segment Information - Segment Financial Information for Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,330	$ 1,180
Operating Expenses	1,157	1,047
Operating Income	173	133
Interest expense	65	67
Income Tax Expense (Benefit)	46	185
Total Assets (excluding Assets Held for Disposition)	15,004		14,848
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,330	1,180
Operating Expenses	1,157	1,047
Operating Income	173	133
Interest expense	65	67
Other Income	13	8
Income Tax Expense (Benefit)	46	185
Net Income (Loss) from Continuing Operations	75	(111)
Total Assets (excluding Assets Held for Disposition)	15,003	14,764
Construction Expenditures	282	296
Power Delivery [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,272	1,124
Operating Expenses	1,103	1,001
Operating Income	169	123
Interest expense	55	56
Other Income	12	6
Income Tax Expense (Benefit)	47	15
Net Income (Loss) from Continuing Operations	79	58
Total Assets (excluding Assets Held for Disposition)	13,438	12,453
Construction Expenditures	264	282
Pepco Energy Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenue	60	56
Operating Expenses	60	54
Operating Income		2
Interest expense
Other Income		1
Income Tax Expense (Benefit)		1
Net Income (Loss) from Continuing Operations		2
Total Assets (excluding Assets Held for Disposition)	286	346
Construction Expenditures		1
Corporate and Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(2)
Operating Expenses	(6)	(8)
Operating Income	4	8
Interest expense	10	11
Other Income	1	1
Income Tax Expense (Benefit)	(1)	169
Net Income (Loss) from Continuing Operations	(4)	(171)
Total Assets (excluding Assets Held for Disposition)	1,279	1,965
Construction Expenditures	$ 18	$ 13