Segment Information - Segment Financial Information for Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,053	$ 1,070	$ 1,865	$ 2,206
Operating Expenses	921	933	1,969	1,943
Operating Income	132	137	(104)	263
Interest Expense	70	65	137	130
Income Tax Expense Related to Continuing Operations	32	29	167	38
Total Assets (excluding Assets Held for Disposition)	14,989		14,989		15,794
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,053	1,070	1,865	2,206
Operating Expenses	921	933	1,969	1,943
Operating Income	132	137	(104)	263
Interest Expense	70	65	137	130
Other Income	8	10	16	18
Income Tax Expense Related to Continuing Operations	32	29	167	38
Net Income (Loss) from Continuing Operations	38	53	(392)	113
Total Assets (excluding Assets Held for Disposition)	14,975	15,365	14,975	15,365
Construction Expenditures	320	298	616	589
Operating Segments [Member] | Power Delivery [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,006	984	2,130	2,039
Operating Expenses	866	860	1,867	1,814
Operating Income	140	124	263	225
Interest Expense	58	53	114	106
Other Income	7	8	13	16
Income Tax Expense Related to Continuing Operations	33	25	48	34
Net Income (Loss) from Continuing Operations	56	54	114	101
Total Assets (excluding Assets Held for Disposition)	12,535	11,734	12,535	11,734
Construction Expenditures	281	285	563	565
Operating Segments [Member] | Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Operating Revenue	49	76	106	148
Operating Expenses	47	77	101	145
Operating Income	2	(1)	5	3
Interest Expense				1
Other Income			1
Income Tax Expense Related to Continuing Operations	1		2	1
Net Income (Loss) from Continuing Operations	1	(1)	4	1
Total Assets (excluding Assets Held for Disposition)	350	480	350	480
Construction Expenditures		5	1	10
Operating Segments [Member] | Other Non-Regulated [Member]
Segment Reporting Information [Line Items]
Operating Revenue	3	14	(365)	27
Operating Expenses	18	2	18	3
Operating Income	(15)	12	(383)	24
Interest Income	1	1	2	2
Interest Expense		4	1	7
Other Income			1	1
Income Tax Expense Related to Continuing Operations	1	2	54	2
Net Income (Loss) from Continuing Operations	(15)	7	(436)	17
Total Assets (excluding Assets Held for Disposition)	765	1,499	765	1,499
Preferred Stock Dividends			1	1
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(5)	(4)	(6)	(8)
Operating Expenses	(10)	(6)	(17)	(19)
Operating Income	5	2	11	11
Interest Income	(1)	(1)	(2)	(2)
Interest Expense	12	8	22	16
Other Income	1	2	1	1
Income Tax Expense Related to Continuing Operations	(3)	2	63	1
Net Income (Loss) from Continuing Operations	(4)	(7)	(74)	(6)
Total Assets (excluding Assets Held for Disposition)	1,325	1,652	1,325	1,652
Construction Expenditures	39	8	52	14
Preferred Stock Dividends			$ (1)	$ (1)