Segment Information - Segment Financial Information for Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,313	$ 1,344	$ 3,760	$ 3,575
Operating Expenses	1,147	1,109	3,270	3,062
Operating Income	166	235	490	513
Interest and dividend income
Interest Expense	68	68	200	205
Other Income (Loss)	15	8	42	24
Income Tax Expense (Benefit)	34	65	125	280
Net Income from Continuing Operations	79	110	207	52
Total Assets (excluding Assets Held for Disposition)	15,298	14,910	15,298	14,910	14,848
Construction Expenditures	293	327	846	943
Power Delivery [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,242	1,298	3,554	3,428
Operating Expenses	1,021	1,067	3,005	2,934
Operating Income	221	231	549	494
Interest and dividend income
Interest Expense	58	58	169	172
Other Income (Loss)	14	8	39	21
Income Tax Expense (Benefit)	65	67	157	115
Net Income from Continuing Operations	112	114	262	228
Total Assets (excluding Assets Held for Disposition)	13,697	12,790	13,697	12,790
Construction Expenditures	272	293	789	856
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(2)	(2)	(6)	(7)
Operating Expenses		(8)	2	(23)
Operating Income	(2)	6	(8)	16
Interest and dividend income
Interest Expense	9	9	30	32
Other Income (Loss)		(1)	1	1
Income Tax Expense (Benefit)	(5)	(1)	(7)	164
Net Income from Continuing Operations	(6)	(3)	(30)	(179)
Total Assets (excluding Assets Held for Disposition)	1,346	1,779	1,346	1,779
Construction Expenditures	20	33	55	85
Pepco Energy Services [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenue	73	48	212	154
Operating Expenses	126	50	263	151
Operating Income	(53)	(2)	(51)	3
Interest and dividend income
Interest Expense	1	1	1	1
Other Income (Loss)	1	1	2	2
Income Tax Expense (Benefit)	(26)	(1)	(25)	1
Net Income from Continuing Operations	(27)	(1)	(25)	3
Total Assets (excluding Assets Held for Disposition)	255	341	255	341
Construction Expenditures	$ 1	$ 1	$ 2	$ 2