Quarterly Financial Information (Schedule Of Quarterly Financial Information) (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, 2010	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Quarterly Financial Information [Line Items]
Total Operating Revenue	$ 1,134		$ 1,476		$ 1,179		$ 1,292		$ 1,253		$ 1,648		$ 1,412		$ 1,638			$ 5,081		$ 5,951		$ 7,040
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 Income	115		264		152		139		91		195		202		149			670		637		624
Other Expenses	(58)		(59)		(55)		(57)		(62)		(60)		(53)		(53)			(229)		(228)		(474)
Income (Loss) Before Income Tax Expense (Benefit)	57		205		97		82		29		135		149		96			441		409		150
Income Tax Expense (Benefit)Related to Continuing Operations	14		93	[4]	35		14		6		55		54	[5]	34			156		149		11
Income Tax (Benefit) Expense																	15
Net income from continuing operations									23		80		95	[3]	62			285		260		139
Income (Loss) From Discontinued Operations, net of taxes									(4)				(1)		2			0		(3)		(107)
NET INCOME	43		112	[2]	62		68		19		80		94		64			285		257		32
Basic and Diluted Earnings Per Share of Common Stock
Earnings Per Share of Common Stock from Continuing Operations									$ 0.10		$ 0.35		$ 0.42		$ 0.27					$ 1.15
Earnings (Loss) Per Share of Common Stock from Discontinued Operations									$ (0.02)						$ 0.01					$ (0.01)
Basic and Diluted Earnings Per Share of Common Stock									$ 0.08		$ 0.35		$ 0.42		$ 0.28					$ 1.14
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	$ 0.18		$ 0.49		$ 0.27		$ 0.30											$ 1.24		$ 1.14		$ 0.14
Cash Dividends Per Share of Common Stock	$ 0.27		$ 0.27		$ 0.27		$ 0.27		$ 0.27		$ 0.27		$ 0.27		$ 0.27			$ 1.08		$ 1.08		$ 1.08
Potomac Electric Power Co [Member]
Quarterly Financial Information [Line Items]
Total Operating Revenue	445		582		456		465		435		603		506		534			1,948		2,078		2,288
Total Operating Expenses	390		475		401		425		400		521		454		491			1,691		1,866		2,058
Operating Income	55		107		55		40		35		82		52		43			257		212		230
Other Expenses	(20)		(22)		(20)		(21)		(20)		(21)		(18)		(18)			(83)		(77)		(85)
Income (Loss) Before Income Tax Expense (Benefit)	35		85		35		19		15		61		34		25			174		135		145
Income Tax Expense (Benefit)Related to Continuing Operations																		48		36		37
Income Tax (Benefit) Expense	10		35		8		(5)	[6]	4	[7]	23	[7]	2	[7]	7	[7]		48		36	[7]
NET INCOME	25		50		27		24		11		38		32		18			126		99		108
Delmarva Power & Light Co/De [Member]
Quarterly Financial Information [Line Items]
Total Operating Revenue	301		340		259		333		294		326		284		400			1,233		1,304		1,400
Total Operating Expenses	263		297		229		290		259		297		248		351			1,079		1,155		1,287
Operating Income	38		43		30		43		35		29		36		49			154		149		113
Other Expenses	(11)		(10)		(8)		(8)		(10)		(8)		(9)		(9)			(37)		(36)		(37)
Income (Loss) Before Income Tax Expense (Benefit)	27		33		22		35		25		21		27		40			117		113		76
Income Tax Expense (Benefit)Related to Continuing Operations																		44		42		31
Income Tax (Benefit) Expense	10		11		9		14		10	[8]	10	[8]	5	[8]	17	[8]		44		42	[8]
NET INCOME	17		22		13		21		15		11		22		23			73		71		45
Atlantic City Electric Co [Member]
Quarterly Financial Information [Line Items]
Total Operating Revenue	259		413		270		256		250		399		304		315			1,198		1,268		1,430
Total Operating Expenses	246		364		230		239		237		347		256		289			1,079		1,129		1,270
Operating Income	13		49		40		17		13		52		48		26			119		139		160
Other Expenses	(17)		(16)		(17)		(16)		(18)		(18)		(16)		(15)			(66)		(67)		(64)
Income (Loss) Before Income Tax Expense (Benefit)	(4)		33		23		1		(5)		34		32		11			53		72		96
Income Tax Expense (Benefit)Related to Continuing Operations																		18		33		43
Income Tax (Benefit) Expense	(3)		13		9		(1)		(3)	[9]	17	[9]	14	[9]	5	[9]		18		33	[9]
NET INCOME	$ (1)		$ 20		$ 14		$ 2		$ (2)		$ 17		$ 18		$ 6			$ 35		$ 39		$ 53

[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 tax benefits of $10 million (after-tax), primarily related to the settlement of an uncertain tax position with the IRS related to the methodology used historically to calculate deductible mixed service costs and the expiration of the statute of limitations associated with an uncertain tax position.

[7] Includes tax benefits of $5 million (after-tax) associated with an interest benefit related to federal tax liabilities and an additional tax benefit of $4 million (after-tax) related to the filing of amended state tax returns, each recorded in the second quarter.

[8] Includes tax benefits of $4 million (after-tax) associated with an interest benefit related to federal tax liabilities in the second quarter and an additional tax expense of $1 million (after-tax) resulting from a recalculation of interest on uncertain tax positions for open tax years in the third quarter.

[9] Includes tax expense of $1 million (after-tax) associated with interest related to federal tax liabilities in the second quarter and an additional tax expense of $3 million (after-tax) resulting from a recalculation of interest on uncertain tax positions for open tax years in the third quarter.