Income Taxes (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Income Taxes [Line Items]
Consolidated effective tax rates		36.10%	36.20%	27.40%	35.90%
Reversal of permanent tax benefits			$ 22		$ 22
Income Tax Settlement			17		17
Income tax refunds received			5
Income recognized related to filed amended return, net of taxes			4
State tax benefit related to prior years' asset dispositions			4		4
Potomac Electric Power Co [Member]
Income Taxes [Line Items]
Consolidated effective tax rates		22.90%	5.80%	5.60%	15.30%
Income Tax Settlement			5		5
Income tax refunds received			5
State tax benefit related to prior years' asset dispositions			4		4
Other, net	3
Atlantic City Electric Co [Member]
Income Taxes [Line Items]
Consolidated effective tax rates		39.10%	43.80%	33.30%	44.20%
Income Tax Settlement			1
Deferred tax adjustment			1
Delmarva Power & Light Co/De [Member]
Income Taxes [Line Items]
Consolidated effective tax rates		40.90%	18.50%	40.40%	32.80%
Income Tax Settlement			4		4
Deferred tax adjustment			$ 1