Segment Information - Segment Financial Information for Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,118	$ 1,313	$ 1,117	$ 1,330	$ 1,091	$ 1,344	$ 1,051	$ 1,180	$ 4,878	$ 4,666	$ 4,625
Operating Expenses	1,004	1,147	966	1,157	936	1,109	906	1,047	4,274	3,998	4,084
Operating Income (Loss)	114	166	151	173	155	235	145	133	604	668	541
Interest Expense									268	273	256
Other Income									44	34	36
Income Tax Expense (Benefit)	13	34	45	46	39	65	30	185	138	319	103
Net Income from Continuing Operations					58	110	53	(111)	242	110	218
Total Assets	15,667				14,848				15,667	14,848	14,519
Construction Expenditures									1,223	1,310	1,216
Interest Income											1
Impairment Losses											(1)
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue									(7)	(9)	(9)
Operating Expenses									4	(31)	(34)
Operating Income (Loss)									(11)	22	25
Interest Expense									41	44	35
Other Income									2	3	3
Income Tax Expense (Benefit)									(11)	163
Net Income from Continuing Operations									(39)	(182)	(9)
Total Assets	1,704				1,486				1,704	1,486	2,028
Construction Expenditures									76	112	37
Interest Income											(1)
Impairment Losses											(1)
Operating Segments [Member] | Power Delivery [Member]
Segment Reporting Information [Line Items]
Operating Revenue									4,607	4,472	4,378
Operating Expenses									3,916	3,828	3,847
Operating Income (Loss)									691	644	531
Interest Expense									226	228	219
Other Income									40	28	32
Income Tax Expense (Benefit)									185	155	110
Net Income from Continuing Operations									320	289	235
Total Assets	13,719				13,027				13,719	13,027	12,149
Construction Expenditures									1,144	1,194	1,168
Interest Income											1
Operating Segments [Member] | Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Operating Revenue									278	203	256
Operating Expenses									354	201	271
Operating Income (Loss)									(76)	2	(15)
Interest Expense									1	1	2
Other Income									2	3	1
Income Tax Expense (Benefit)									(36)	1	(7)
Net Income from Continuing Operations									(39)	3	(8)
Total Assets	244				335				244	335	342
Construction Expenditures									3	4	11
Interest Income											$ 1