Segment Information - Segment Financial Information for Continuing Operations (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,150	$ 1,362	$ 1,140	$ 1,371	$ 1,118	$ 1,313	$ 1,117	$ 1,330	$ 5,023	$ 4,878	$ 4,666
Operating Expenses	941	1,179	1,001	1,229	1,004	1,147	966	1,157	4,350	4,274	3,998
Operating Income (Loss)	209	183	139	142	114	166	151	173	673	604	668
Interest Expense									280	268	273
Other income									54	44	34
Income Tax Expense (Benefit)	23	49	27	30	13	$ 34	$ 45	$ 46	129	138	319
Net Income (Loss) from Continuing Operations	121	$ 91	$ 53	$ 53					318	242	110
Total Assets	16,326				15,589				16,326	15,589	14,778
Construction Expenditures									1,230	1,223	1,310
Power Delivery [Member]
Segment Reporting Information [Line Items]
Operating Revenue									4,805	4,607	4,472
Operating Expenses									4,124	3,916	3,828
Operating Income (Loss)									681	691	644
Interest Expense									238	226	228
Other income									36	40	28
Income Tax Expense (Benefit)									177	185	155
Net Income (Loss) from Continuing Operations									302	320	289
Total Assets	14,413				13,636				14,413	13,636	12,868
Construction Expenditures									1,196	1,144	1,194
Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Operating Revenue									223	278	203
Operating Expenses									224	354	201
Operating Income (Loss)									(1)	(76)	2
Interest Expense										1	1
Other income									1	2	3
Income Tax Expense (Benefit)									(4)	(36)	1
Net Income (Loss) from Continuing Operations									4	(39)	3
Total Assets	221				249				221	249	337
Construction Expenditures									3	3	4
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue									(5)	(7)	(9)
Operating Expenses									2	4	(31)
Operating Income (Loss)									(7)	(11)	22
Interest Expense									42	41	44
Other income									17	2	3
Income Tax Expense (Benefit)									(44)	(11)	163
Net Income (Loss) from Continuing Operations									12	(39)	(182)
Total Assets	$ 1,692				$ 1,704				1,692	1,704	1,573
Construction Expenditures									$ 31	$ 76	$ 112