Schedule I - Condensed Financial Information Of Parent Company (Statements Of Income) (Detail) (USD $) In Millions, except Per Share data, 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, 2012		Dec. 31, 2011	Dec. 31, 2010
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
Other operation and maintenance														911		914	884
Total 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 LOSS	115		264		152		139		91	195	202		149	670		637	624
OTHER INCOME (EXPENSES)
Interest expense														(265)		(254)	(306)
Loss on extinguishment of debt																	(189)
Income from equity investments														1		(3)	(1)
Impairment Losses														(12)
Total Other Expenses	(58)		(59)		(55)		(57)		(62)	(60)	(53)		(53)	(229)		(228)	(474)
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAX EXPENSE	57		205		97		82		29	135	149		96	441		409	150
INCOME TAX BENEFIT RELATED TO CONTINUING OPERATIONS	14		93	[4]	35		14		6	55	54	[5]	34	156		149	11
Net income from continuing operations									23	80	95	[3]	62	285		260	139
INCOME (LOSS) FROM DISCONTINUED OPERATIONS, NET OF INCOME TAXES									(4)		(1)		2	0		(3)	(107)
NET INCOME	43		112	[2]	62		68		19	80	94		64	285		257	32
COMPREHENSIVE INCOME														300		300	167
EARNINGS PER SHARE
Basic earnings per share of common stock from Continuing Operations														$ 1.25		$ 1.15	$ 0.62
Basic loss per share of common stock from discontinued operations																$ (0.01)	$ (0.48)
Basic earnings per share of common stock	$ 0.18		$ 0.49		$ 0.27		$ 0.30							$ 1.25		$ 1.14	$ 0.14
Diluted earnings per share of common stock from Continuing Operations														$ 1.24		$ 1.15	$ 0.62
Diluted loss per share of common stock from Discontinued Operations																$ (0.01)	$ (0.48)
Diluted earnings per share of common stock	$ 0.18		$ 0.49		$ 0.27		$ 0.30							$ 1.24		$ 1.14	$ 0.14
Parent Company [Member]
OPERATING REVENUE
Operating Expenses
Other operation and maintenance														1		1	5
Total operating expenses														1		1	5
OPERATING LOSS														(1)		(1)	(5)
OTHER INCOME (EXPENSES)
Interest expense														(33)		(29)	(72)
Loss on extinguishment of debt																	(189)
Income from equity investments														304		281	287
Impairment Losses																(5)
Total Other Expenses														271		247	26
INCOME FROM CONTINUING OPERATIONS BEFORE INCOME TAX EXPENSE														270		246	21
INCOME TAX BENEFIT RELATED TO CONTINUING OPERATIONS														(15)		(14)	(118)
Net income from continuing operations														285		260	139
INCOME (LOSS) FROM DISCONTINUED OPERATIONS, NET OF INCOME TAXES																(3)	(107)
NET INCOME														285		257	32
COMPREHENSIVE INCOME														$ 300		$ 300	$ 167
EARNINGS PER SHARE
Basic earnings per share of common stock from Continuing Operations														$ 1.25		$ 1.15	$ 0.62
Basic loss per share of common stock from discontinued operations																$ (0.01)	$ (0.48)
Basic earnings per share of common stock														$ 1.25		$ 1.14	$ 0.14
Diluted earnings per share of common stock from Continuing Operations														$ 1.24		$ 1.15	$ 0.62
Diluted loss per share of common stock from Discontinued Operations																$ (0.01)	$ (0.48)
Diluted earnings per share of common stock														$ 1.24		$ 1.14	$ 0.14

[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.