Segment Information (Segment Financial Information For Continuing Operations) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011		Mar. 31, 2011	Dec. 31, 2010		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Segment Reporting Information [Line Items]
OPERATING REVENUE	$ 1,134		$ 1,476		$ 1,179		$ 1,292		$ 1,253		$ 1,648	$ 1,412		$ 1,638			$ 5,081		$ 5,951		$ 7,040
Operating Expenses	1,019	[1]	1,212	[1],[2]	1,027	[1]	1,153	[1]	1,162		1,453	1,210	[3]	1,489			4,411	[1]	5,314		6,416
Operating Income	115		264		152		139		91		195	202		149			670		637		624
Interest Expense																	265		254		306
Impairment Losses																	(12)
Income Tax Expense															15
Total Assets	15,776								14,910								15,776		14,910
Goodwill	1,407								1,407						1,407		1,407		1,407		1,407
Depreciation and amortization																	454		426		393
Impairment losses, pre-tax																	12
Impairment losses, after-tax																	7
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		3
Reversal of previously recognized tax benefits	16																16
Income Tax Expense Related to Continuing Operations	14		93	[4]	35		14		6		55	54	[5]	34			156		149		11
Tax benefits																	(76)		9		(270)
Loss on extinguishment of debt																					(189)
Restructuring charge																					30
Divestiture-related claims expense																					11
Loss on extinguishment of debt																					174
Loss on extinguishment of debt, Net																					104
Losses on treasury rate locks reclassified into income																			1		18
Losses on treasury rate locks reclassified into income, net																					9
Reversal of accrued interest income on uncertain, effectively settled tax positions																					12
State tax benefits																	(39)		4		(50)
Write off of deferred tax asset related to Medicare Part D subsidy, ultimately offset against state tax benefits																					3
Subsidiaries [Member]
Segment Reporting Information [Line Items]
Impairment losses, pre-tax																	12
Impairment losses, after-tax																	7
State tax benefits																					(14)
Power Delivery [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUE																	4,378		4,650		5,114
Operating Expenses																	3,847	[6]	4,150	[7]	4,611	[10],[8],[9]
Operating Income																	531		500		503
Interest Income																	1		1		2
Interest Expense																	219		208		207
Other Income																	32		29		20
Income Tax Expense																	110
Net Income (Loss) from Continuing Operations																	235		210		206
Total Assets	12,149								11,008						10,621		12,149		11,008		10,621
Construction Expenditures																	1,168		888		765
Goodwill	1,400								1,400						1,400		1,400		1,400		1,400
Depreciation and amortization																	416		394		357
Income Tax Expense Related to Continuing Operations																			112	[11]	112	[12]
Tax benefits																			14
Loss on extinguishment of debt
Restructuring charge																					29
Intersegment [Member]
Segment Reporting Information [Line Items]
Operating Expenses																	(10)		(15)		(10)
Interest Income																	(21)		(22)		(36)
Interest Expense																	(18)		(22)		(36)
Preferred Stock Dividends																	(3)		(3)		(3)
Operating Revenue																	(11)		(16)		(12)
State income tax benefits associated with loss on extinguishment of debt																					(17)
Pepco Energy Services [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUE																	662		1,269		1,884
Operating Expenses																	634	[1],[6]	1,237	[7]	1,813	[8],[9]
Operating Income																	28		32		71
Interest Income																	1		1		1
Interest Expense																	1		3		16
Other Income																	1		3		2
Income Tax Expense																	11
Net Income (Loss) from Continuing Operations																	18		24		36
Total Assets	362								565						623		362		565		623
Construction Expenditures																	11		14		7
Depreciation and amortization																	14		17		24
Income Tax Expense Related to Continuing Operations																			9	[11]	22
Loss on extinguishment of debt
Other Non-Regulated [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUE																	52		48		54
Operating Expenses																	(34)	[13],[6]	(30)	[14],[7]	6	[8],[9]
Operating Income																	86		78		48
Interest Income																	4		4		3
Interest Expense																	11		13		12
Impairment Losses																	(1)
Other Income																			(4)		(2)
Preferred Stock Dividends																	3		3		3
Income Tax Expense																	35	[15]
Net Income (Loss) from Continuing Operations																	40	[13]	35	[14]	25
Total Assets	1,361								1,499						1,537		1,361		1,499		1,537
Depreciation and amortization																	2		2		1
Reversal of previously recognized tax benefits									22										22
Income Tax Expense Related to Continuing Operations																			27	[11]	9
Loss on extinguishment of debt
Corporate And Other [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUE																	(11)	[16]	(16)	[16]	(12)	[16]
Operating Expenses																	(36)	[16],[6]	(43)	[16],[7]	(14)	[16],[8],[9]
Operating Income																	25	[16]	27	[16]	2	[16]
Interest Income																	(5)	[16]	(5)	[16]	(6)	[16]
Interest Expense																	34	[16]	30	[16]	71	[16]
Other Income																	3	[16]	2	[16]	1	[16]
Preferred Stock Dividends																	(3)	[16]	(3)	[16]	(3)	[16]
Net Income (Loss) from Continuing Operations																	(8)	[16]	(9)	[16]	(128)	[16]
Total Assets	1,904	[16]							1,838	[16]					1,582	[16]	1,904	[16]	1,838	[16]	1,582	[16]
Construction Expenditures																	37	[16]	39	[16]	30	[16]
Depreciation and amortization																	22		13		11
Impairment Losses																			(5)	[16]
Income Tax Expense Related to Continuing Operations																			1	[11],[16]	(132)	[16],[17]
Loss on extinguishment of debt																					(189)	[16],[18]
Restructuring charge																					1
Losses on treasury rate locks reclassified into income																					15
PHI Consolidated [Member]
Segment Reporting Information [Line Items]
OPERATING REVENUE																	5,081		5,951		7,040
Operating Expenses																	4,411	[6]	5,314	[7]	6,416	[8],[9]
Operating Income																	670		637		624
Interest Income																	1		1
Interest Expense																	265		254		306
Impairment Losses																	(1)
Other Income																	36		30		21
Income Tax Expense																	156
Net Income (Loss) from Continuing Operations																	285		260		139
Total Assets	15,776								14,910						14,363		15,776		14,910		14,363
Construction Expenditures																	1,216		941		802
Impairment Losses																			(5)
Income Tax Expense Related to Continuing Operations																			149	[11]	11
Loss on extinguishment of debt																					$ (189)

[1] Includes impairment losses of $12 million pre-tax ($7 million after-tax) at Pepco Energy Services associated primarily with investments in landfill gas-fired electric generation facilities, and the combustion turbines at Buzzard Point.

[2] Includes $39 million pre-tax ($9 million after-tax) gain from the early termination of cross-border energy leases.

[3] Includes $39 million pre-tax ($3 million after-tax) gain from the early termination of cross-border energy leases.

[4] Includes a $16 million charge related to the recognition of the tax consequences associated with the early termination of cross-border energy leases.

[5] Includes tax benefits of $14 million in the second quarter primarily associated with an interest benefit related to federal tax liabilities and a $22 million charge related to the recognition of the tax consequences associated with the early termination of cross-border energy leases.

[6] Includes depreciation and amortization expense of $454 million, consisting of $416 million for Power Delivery, $14 million for Pepco Energy Services, $2 million for Other Non-Regulated and $22 million for Corporate and Other.

[7] Includes depreciation and amortization expense of $426 million, consisting of $394 million for Power Delivery, $17 million for Pepco Energy Services, $2 million for Other Non-Regulated, and $13 million for Corporate and Other.

[8] Includes depreciation and amortization expense of $393 million, consisting of $357 million for Power Delivery, $24 million for Pepco Energy Services, $1 million for Other Non-Regulated, and $11 million for Corporate and Other.

[9] Includes restructuring charge of $30 million, consisting of $29 million for Power Delivery and $1 million for Corporate and Other.

[10] Includes $11 million expense related to effects of Pepco divestiture-related claims.

[11] Includes tax benefits of $14 million for Power Delivery primarily associated with an interest benefit related to federal tax liabilities and a $22 million charge for Other Non-Regulated related to the recognition of the tax consequences associated with the early termination of cross-border energy leases held in trust.

[12] Includes $12 million of net Federal and state income tax benefits primarily related to adjustments of accrued interest on uncertain and effectively settled tax positions.

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

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

[15] Includes a $16 million charge related to the recognition of the tax consequences associated with the early termination of finance leases held in trust.

[16] 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, $(10) million for Operating Expenses, $(21) million for Interest Income, $(18) million for Interest Expense and $(3) million for Preferred Stock Dividends.

[17] Includes $14 million of state tax benefits resulting from the restructuring of certain PHI subsidiaries and $17 million of state income tax benefits associated with the loss on extinguishment of debt, partially offset by a charge of $3 million to write off deferred tax assets related to the subsidy pursuant to the prescription drug benefit (Medicare Part D) under the Medicare Prescription Drug Improvement and Modernization Act of 2003 (the Medicare Act).

[18] Includes $174 million ($104 million after-tax) related to loss on extinguishment of debt and $15 million ($9 million after-tax) related to the reclassification of treasury rate lock losses from AOCL to income related to cash tender offers for debt made in 2010.