Segment Information - Segment Financial Information (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,362			$ 1,313	$ 3,873	$ 3,760
Operating Expenses	1,179			1,147	3,409	3,270
Operating Income	183			166	464	490
Interest Expense	71			68	210	200
Other income	28			15	49	42
Income Tax Expense (Benefit)	49			34	106	125
Net Income	91	$ 53	$ 53	79	197	207
Total Assets	16,557			15,298	16,557	15,298	$ 15,667
Construction Expenditures	293			293	855	846
Operating Segments [Member] | Power Delivery [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,316			1,242	3,707	3,554
Operating Expenses	1,131			1,021	3,238	3,005
Operating Income	185			221	469	549
Interest Expense	59			58	177	169
Other income	11			14	32	39
Income Tax Expense (Benefit)	49			65	113	157
Net Income	88			112	211	262
Total Assets	14,330			13,697	14,330	13,697
Construction Expenditures	286			272	832	789
Operating Segments [Member] | Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Operating Revenue	47			73	170	212
Operating Expenses	49			126	172	263
Operating Income	(2)			(53)	(2)	(51)
Interest Expense				1		1
Other income				1		2
Income Tax Expense (Benefit)	(2)			(26)	(7)	(25)
Net Income				(27)	5	(25)
Total Assets	218			255	218	255
Construction Expenditures				1	2	2
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(1)			(2)	(4)	(6)
Operating Expenses	(1)				(1)	2
Operating Income				(2)	(3)	(8)
Interest Expense	12			9	33	30
Other income	17				17	1
Income Tax Expense (Benefit)	2			(5)		(7)
Net Income	3			(6)	(19)	(30)
Total Assets	2,009			1,346	2,009	1,346
Construction Expenditures	$ 7			$ 20	$ 21	$ 55