Income Taxes (Reconciliation Of Effective Income Tax Rate From Continuing Operations) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 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	5.30%	4.00%	5.40%	4.50%
Asset removal costs	(4.00%)	(1.30%)	(3.80%)	(1.20%)
Change in estimates and interest related to uncertain and effectively settled tax positions	2.80%	(11.40%)	(5.80%)	(6.10%)
Cross-border energy lease investments	(1.10%)	14.10%	(1.20%)	8.20%
State tax benefit related to prior years' asset dispositions		(2.70%)		(1.60%)
Other, net	(1.90%)	(1.50%)	(2.20%)	(2.90%)
Consolidated income tax expense	36.10%	36.20%	27.40%	35.90%
Income tax at Federal statutory rate	$ 34	$ 52	$ 63	$ 86
State income taxes, net of Federal effect	5	6	10	11
Asset removal costs	(4)	(2)	(7)	(3)
Change in estimates and interest related to uncertain and effectively settled tax positions	3	(17)	(10)	(15)
Cross-border energy lease investments	(1)	21	(2)	20
State tax benefit related to prior years' asset dispositions		(4)		(4)
Other, net	(2)	(2)	(5)	(7)
Consolidated income tax expense	35	54	49	88
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	5.60%	4.70%	5.70%	4.60%
Asset removal costs	(11.50%)	(4.40%)	(12.80%)	(4.20%)
Change in estimates and interest related to uncertain and effectively settled tax positions	(3.50%)	(12.10%)	(20.20%)	(6.60%)
Permanent differences related to deferred compensation funding	(0.90%)	(1.20%)	(0.90%)	(2.50%)
State tax benefit related to prior years' asset dispositions		(12.40%)		(7.10%)
Other, net	(1.80%)	(3.80%)	(1.20%)	(3.90%)
Consolidated income tax expense	22.90%	5.80%	5.60%	15.30%
Income tax at Federal statutory rate	12	12	19	21
State income taxes, net of Federal effect	2	2	3	3
Asset removal costs	(4)	(2)	(7)	(3)
Change in estimates and interest related to uncertain and effectively settled tax positions	(1)	(4)	(11)	(4)
Permanent differences related to deferred compensation			(1)	(2)
State tax benefit related to prior years' asset dispositions		(4)		(4)
Other, net	(1)	(2)		(2)
Consolidated income tax expense	8	2	3	9
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	5.10%	5.20%	5.40%	6.00%
Change in estimates and interest related to uncertain and effectively settled tax positions		(18.50%)	(0.20%)	(7.50%)
Deferred tax adjustment		(3.70%)		(1.50%)
Depreciation	0.50%	3.70%		1.50%
Other, net	0.30%	(3.20%)	0.20%	(0.70%)
Consolidated income tax expense	40.90%	18.50%	40.40%	32.80%
Income tax at Federal statutory rate	8	10	20	24
State income taxes, net of Federal effect	1	1	3	4
Change in estimates and interest related to uncertain and effectively settled tax positions		(5)		(5)
Deferred tax adjustment		(1)		(1)
Depreciation		1		1
Other, net		(1)		(1)
Consolidated income tax expense	9	5	23	22
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	4.20%	6.60%	4.00%	7.00%
Change in estimates and interest related to uncertain and effectively settled tax positions	0.80%	1.30%	(4.00%)	1.40%
Deferred tax adjustment		3.10%	(0.40%)	2.30%
Other, net	(0.90%)	(2.20%)	(1.30%)	(1.50%)
Consolidated income tax expense	39.10%	43.80%	33.30%	44.20%
Income tax at Federal statutory rate	8	11	8	15
State income taxes, net of Federal effect	1	2	1	3
Change in estimates and interest related to uncertain and effectively settled tax positions			(1)	1
Deferred tax adjustment		1		1
Other, net				(1)
Consolidated income tax expense	$ 9	$ 14	$ 8	$ 19