Income Taxes (Reconciliation Of Effective Income Tax Rate From Continuing Operations) (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
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	35.00%	35.00%		35.00%	35.00%
State income taxes, net of Federal effect	4.40%	6.70%		5.00%	5.00%
Asset removal costs	(0.50%)	(1.50%)		(2.10%)	(1.10%)
Change in estimates and interest related to uncertain and effectively settled tax positions		3.70%		(2.60%)	(2.90%)
Cross-border energy lease investments	7.30%	(3.70%)		3.40%	3.90%
Other, net	(0.80%)	0.50%		(1.70%)	(2.30%)
Consolidated income tax expense	45.40%	40.70%		37.00%	37.60%
Income tax at Federal statutory rate	$ 72	$ 47		$ 134	$ 133
State income taxes, net of Federal effect	9	9		19	19
Asset removal costs	(1)	(2)		(8)	(4)
Change in estimates and interest related to uncertain and effectively settled tax positions		5		(10)	(11)
Cross-border energy lease investments	15	(5)		13	15
Other, net	(2)	1		(6)	(9)
Consolidated income tax expense	93	55		142	143
Potomac Electric Power Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	35.00%	35.00%		35.00%	35.00%
State income taxes, net of Federal effect	5.90%	6.10%		5.80%	5.30%
Asset removal costs	(1.20%)	(3.00%)		(5.80%)	(3.70%)
Change in estimates and interest related to uncertain and effectively settled tax positions		1.30%		(7.90%)	(2.70%)
Permanent differences related to deferred compensation funding		(0.30%)		(0.70%)	(1.40%)
State tax benefit related to prior years' asset dispositions					(3.50%)
Tax credits				(0.70%)
Other, net	1.50%	(1.40%)		1.60%	(2.30%)
Consolidated income tax expense	41.20%	37.70%		27.30%	26.70%
Income tax at Federal statutory rate	30	21		49	42
State income taxes, net of Federal effect	5	4		8	6
Asset removal costs	(1)	(2)		(8)	(4)
Change in estimates and interest related to uncertain and effectively settled tax positions		1		(11)	(4)
Permanent differences related to deferred compensation funding				(1)	(2)
State tax benefit related to prior years' asset dispositions			4		(4)
Tax credits				(1)
Other, net	1	(1)		2	(2)
Consolidated income tax expense	35	23		38	32
Delmarva Power & Light Co/De [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	35.00%	35.00%		35.00%	35.00%
State income taxes, net of Federal effect	6.10%	5.20%		5.60%	5.30%
Adjustments to prior year taxes	(6.10%)	(4.80%)		(2.20%)	(1.10%)
Change in estimates and interest related to uncertain and effectively settled tax positions		9.50%			(3.10%)
Depreciation	(3.00%)	(0.50%)		(1.10%)
Other, net	1.30%	3.20%		0.50%	0.30%
Consolidated income tax expense	33.30%	47.60%		37.80%	36.40%
Income tax at Federal statutory rate	12	7		32	31
State income taxes, net of Federal effect	2	1		5	5
Adjustments to prior year taxes	(2)	(1)		(2)	(1)
Change in estimates and interest related to uncertain and effectively settled tax positions		2			(3)
Depreciation	(1)			(1)
Other, net		1
Consolidated income tax expense	11	10		34	32
Atlantic City Electric Co [Member]
Income Tax Rate Reconciliation [Line Items]
Income tax at Federal statutory rate	35.00%	35.00%		35.00%	35.00%
State income taxes, net of Federal effect	6.10%	4.40%		5.30%	5.90%
Change in estimates and interest related to uncertain and effectively settled tax positions		10.50%			5.10%
Deferred tax adjustment					1.70%
Other, net	(1.70%)	0.10%		(3.50%)	(0.90%)
Consolidated income tax expense	39.40%	50.00%		36.80%	46.80%
Income tax at Federal statutory rate	11	12		20	27
State income taxes, net of Federal effect	2	2		3	5
Change in estimates and interest related to uncertain and effectively settled tax positions		4			4
Deferred tax adjustment					1
Other, net		(1)		(2)	(1)
Consolidated income tax expense	$ 13	$ 17		$ 21	$ 36