Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Mar. 31, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule of Income Tax [Line Items]
Consolidated effective tax rates from continuing operations	37.10%		39.60%		84.30%	33.30%
Change in estimates and interest related to uncertain tax positions					55
Establishment of valuation allowance on deferred tax assets		101			101
After-tax effect of revised lease rerun		377
Potomac Electric Power Co [Member]
Schedule of Income Tax [Line Items]
Consolidated effective tax rates from continuing operations	37.70%		41.20%		33.00%	27.30%
Additional interest income		5
Additional income tax (expenses) benefit				11
Potomac Electric Power Co [Member] | Interest Expense [Member]
Schedule of Income Tax [Line Items]
After-tax non-cash charge		54
Delmarva Power & Light Co/De [Member]
Schedule of Income Tax [Line Items]
Consolidated effective tax rates from continuing operations	37.80%		33.30%		39.00%	37.80%
Additional interest income		1
After-tax effect of revised lease rerun		377
Delmarva Power & Light Co/De [Member] | Interest Expense [Member]
Schedule of Income Tax [Line Items]
After-tax non-cash charge		54
Atlantic City Electric Co [Member]
Schedule of Income Tax [Line Items]
Consolidated effective tax rates from continuing operations	34.20%		39.40%		25.50%	36.80%
Additional interest income		6
Atlantic City Electric Co [Member] | Interest Expense [Member]
Schedule of Income Tax [Line Items]
After-tax non-cash charge		$ 54