Segment Information - Segment Financial Information for Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,117	$ 1,051	$ 2,447	$ 2,231
Operating Expenses	966	906	2,123	1,953
Operating Income	151	145	324	278
Interest and dividend income	1		1
Interest Expense	67	70	132	137
Other Income (Expense)	13	8	26	16
Income Tax Expense (Benefit)	45	30	91	215
Net Income (Loss) from Continuing Operations	53	53	128	(58)
Total Assets (excluding Assets Held for Disposition)	15,070	14,808	15,070	14,808	14,848
Construction Expenditures	271	320	553	616
Power Delivery [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,040	1,006	2,312	2,130
Operating Expenses	881	866	1,984	1,867
Operating Income	159	140	328	263
Interest Expense	56	58	111	114
Other Income (Expense)	13	7	25	13
Income Tax Expense (Benefit)	45	33	92	48
Net Income (Loss) from Continuing Operations	71	56	150	114
Total Assets (excluding Assets Held for Disposition)	13,471	12,535	13,471	12,535
Construction Expenditures	253	281	517	563
Pepco Energy Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenue	79	49	139	106
Operating Expenses	77	47	137	101
Operating Income	2	2	2	5
Other Income (Expense)	1		1	1
Income Tax Expense (Benefit)	1	1	1	2
Net Income (Loss) from Continuing Operations	2	1	2	4
Total Assets (excluding Assets Held for Disposition)	297	350	297	350
Construction Expenditures	1		1	1
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(2)	(4)	(4)	(5)
Operating Expenses	8	(7)	2	(15)
Operating Income	(10)	3	(6)	10
Interest and dividend income	1		1
Interest Expense	11	12	21	23
Other Income (Expense)	(1)	1		2
Income Tax Expense (Benefit)	(1)	(4)	(2)	165
Net Income (Loss) from Continuing Operations	(20)	(4)	(24)	(176)
Total Assets (excluding Assets Held for Disposition)	1,302	1,923	1,302	1,923
Construction Expenditures	$ 17	$ 39	$ 35	$ 52