Segment Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended					9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Jun. 30, 2011	Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011
Segment Reporting Information [Line Items]
Operating Revenue	$ 1,476		$ 1,648			$ 3,947		$ 4,698
Operating Expenses	1,212	[1]	1,453	[2]		3,392	[3]	4,152	[4]
Operating Income	264		195			555		546
Interest Expense	68		64			198		189
Other Income (Expenses)	9		4			27		23
Income Tax Expense	93		55			142		143	[5]
Net Income (Loss) from Continuing Operations	112		80			242		237
Total Assets	15,622		14,568			15,622		14,568		14,910
Construction Expenditures	299		252			888		639
Goodwill	1,407					1,407				1,407
Depreciation and amortization	122		115			343		325
Impairment losses, pre-tax	2
Impairment losses, After-tax	1
Gain on early termination of finance leases held in trust	39				39	39		39
Gain on early termination of finance leases held in trust,after tax	9					9		3
Reversal of previously recognized tax benefits	16		22			16		22
Federal tax liabilities								14
Power Delivery [Member]
Segment Reporting Information [Line Items]
Operating Revenue	1,335		1,329			3,374		3,671
Operating Expenses	1,136	[1]	1,167	[2]		2,950	[3]	3,255	[4]
Operating Income	199		162			424		416
Interest Income			1					1
Interest Expense	56		53			162		155
Other Income (Expenses)	8		7			24		23
Income Tax Expense	59		51			93		100	[5]
Net Income (Loss) from Continuing Operations	92		66			193		185
Total Assets	12,039		11,015			12,039		11,015
Construction Expenditures	289		239			854		603
Goodwill	1,400		1,400			1,400		1,400
Depreciation and amortization	114		107			313		301
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Operating Expenses	(4)		(6)			(11)		(12)
Interest Income	(7)		(7)			(18)		(17)
Interest Expense	(5)		(6)			(15)		(15)
Preferred Stock Dividends	(1)		(1)			(2)		(2)
Operating Revenue	(3)		(5)			(11)		(13)
Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
Operating Revenue	131		317			544		1,005
Operating Expenses	125	[1],[6]	305	[2]		507	[3],[7]	964	[4]
Operating Income	6		12			37		41
Interest Income	1		1			1		1
Interest Expense			1			1		3
Other Income (Expenses)	1		1			1		3
Income Tax Expense	3		5			15		16	[5]
Net Income (Loss) from Continuing Operations	5		8			23		26
Total Assets	442		611			442		611
Construction Expenditures	1		4			11		11
Depreciation and amortization	2		4			12		13
Impairment losses, pre-tax						5
Impairment losses, After-tax						3
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Operating Revenue	(3)	[8]	(5)	[9]		(11)	[10]	(13)	[11]
Operating Expenses	(11)	[1],[8]	(21)	[2],[9]		(30)	[10],[3]	(33)	[11],[4]
Operating Income	8	[8]	16	[9]		19	[10]	20	[11]
Interest Income	(2)	[8]	(2)	[9]		(4)	[10]	(4)	[11]
Interest Expense	9	[8]	7	[9]		25	[10]	21	[11]
Other Income (Expenses)	1	[8]	(1)	[9]		2	[10]	1	[11]
Preferred Stock Dividends	(1)	[8]	(1)	[9]		(2)	[10]	(2)	[11]
Income Tax Expense			6	[9]		1	[10]	2	[11],[5]
Net Income (Loss) from Continuing Operations	(1)	[8]	1	[9]		(7)	[10]	(4)	[11]
Total Assets	1,658	[10],[8]	1,475	[11],[9]		1,658	[10],[8]	1,475	[11],[9]
Construction Expenditures	9	[8]	9	[9]		23	[10]	25	[11]
Depreciation and amortization	6		4			17		10
Other Non-Regulated [Member]
Segment Reporting Information [Line Items]
Operating Revenue	13		7			40		35
Operating Expenses	(38)	[1],[12]	2	[2]		(35)	[12],[3]	(34)	[13],[4]
Operating Income	51		5			75		69
Interest Income	1					3		2
Interest Expense	3		3			10		10
Other Income (Expenses)	(1)		(3)					(4)
Preferred Stock Dividends	1		1			2		2
Income Tax Expense	31	[14]	(7)			33	[14]	25	[5]
Net Income (Loss) from Continuing Operations	16	[12]	5			33	[12]	30	[13]
Total Assets	1,483		1,467			1,483		1,467
Depreciation and amortization						$ 1		$ 1

[1] Includes depreciation and amortization expense of $122 million, consisting of $114 million for Power Delivery, $2 million for Pepco Energy Services and $6 million for Corporate and Other.

[2] Includes depreciation and amortization expense of $115 million, consisting of $107 million for Power Delivery, $4 million for Pepco Energy Services and $4 million for Corporate and Other.

[3] Includes depreciation and amortization expense of $343 million, consisting of $313 million for Power Delivery, $12 million for Pepco Energy Services, $1 million for Other Non-Regulated and $17 million for Corporate and Other.

[4] Includes depreciation and amortization expense of $325 million, consisting of $301 million for Power Delivery, $13 million for Pepco Energy Services, $1 million for Other Non-Regulated and $10 million for Corporate and Other.

[5] Includes tax benefits of $14 million for Power Delivery primarily associated with an interest benefit related to federal tax liabilities and a $22 million reversal of previously recognized tax benefits for Other Non-Regulated associated with the early termination of finance leases held in trust.

[6] Includes impairment losses of $2 million pre-tax ($1 million after-tax) at Pepco Energy Services associated with the combustion turbines at Buzzard Point.

[7] Includes impairment losses of $5 million pre-tax ($3 million after-tax) at Pepco Energy Services associated primarily with an investment in a landfill gas-fired electric generation facility, and the combustion turbines at Buzzard Point.

[8] Total Assets in this column includes Pepco Holdings' goodwill balance of $1.4 billion, all of which is allocated to Power Delivery for purposes of assessing impairment. Total assets also include capital expenditures related to certain hardware and software expenditures which primarily benefit Power Delivery. These expenditures are recorded as incurred in the Corporate and Other segment and are allocated to Power Delivery once the assets are placed in service. Corporate and Other includes intercompany amounts of $(3) million for Operating Revenue, $(4) million for Operating Expenses, $(7) million for Interest Income, $(5) million for Interest Expense and $(1) million for Preferred Stock Dividends.

[9] Total Assets in this column includes Pepco Holdings' goodwill balance of $1.4 billion, all of which is allocated to Power Delivery for purposes of assessing impairment. Total assets also include capital expenditures related to certain hardware and software expenditures which primarily benefit Power Delivery. These expenditures are recorded as incurred in the Corporate and Other segment and are allocated to Power Delivery once the assets are placed in service. Corporate and Other includes intercompany amounts of $(5) million for Operating Revenue, $(6) million for Operating Expenses, $(7) million for Interest Income, $(6) million for Interest Expense and $(1) million for Preferred Stock Dividends.

[10] Total Assets in this column includes Pepco Holdings' goodwill balance of $1.4 billion, all of which is allocated to Power Delivery for purposes of assessing impairment. Total assets also include capital expenditures related to certain hardware and software expenditures which primarily benefit Power Delivery. These expenditures are recorded as incurred in the Corporate and Other segment and are allocated to Power Delivery once the assets are placed in service. Corporate and Other includes intercompany amounts of $(11) million for Operating Revenue, $(11) million for Operating Expenses, $(18) million for Interest Income, $(15) million for Interest Expense and $(2) million for Preferred Stock Dividends.

[11] Total Assets in this column includes Pepco Holdings' goodwill balance of $1.4 billion, all of which is allocated to Power Delivery for purposes of assessing impairment. Total assets also include capital expenditures related to certain hardware and software expenditures which primarily benefit Power Delivery. These expenditures are recorded as incurred in the Corporate and Other segment and are allocated to Power Delivery once the assets are placed in service. Corporate and Other includes intercompany amounts of $(13) million for Operating Revenue, $(12) million for Operating Expenses, $(17) million for Interest Income, $(15) million for Interest Expense and $(2) million for Preferred Stock Dividends.

[12] Includes $39 million pre-tax ($9 million after-tax) gain from the early termination of finance leases held in trust.

[13] Includes $39 million pre-tax ($3 million after-tax) gain from the early termination of finance leases held in trust.

[14] Includes a $16 million reversal of previously recognized tax benefits associated with the early termination of finance leases held in trust.