Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule Of Income Tax [Line Items]
Consolidated effective tax rates from continuing operations	45.70%		35.40%	(74.20%)	25.20%
State income taxes, net of Federal effect	$ 6		$ 5	$ 10	$ 10
Change in estimates and interest related to uncertain tax positions				70
Tax consequence due to change in intent of foreign investment opportunities				64
Establishment of valuation allowance on deferred tax assets		101		101
After-tax effect of revised lease rerun		377
Interest Expense [Member]
Schedule Of Income Tax [Line Items]
After-tax non-cash charge				70
Potomac Electric Power Co [Member]
Schedule Of Income Tax [Line Items]
Consolidated effective tax rates from continuing operations	35.10%		22.90%	26.80%	5.60%
State income taxes, net of Federal effect	3		2	5	3
After-tax effect of revised lease rerun		377
Additional interest income		5
Potomac Electric Power Co [Member] | Interest Expense [Member]
Schedule Of Income Tax [Line Items]
After-tax non-cash charge		70
Delmarva Power & Light Co/De [Member]
Schedule Of Income Tax [Line Items]
Consolidated effective tax rates from continuing operations	42.90%		40.90%	39.70%	40.40%
State income taxes, net of Federal effect	1		1	3	3
After-tax effect of revised lease rerun		377
Additional interest income		1
Delmarva Power & Light Co/De [Member] | Interest Expense [Member]
Schedule Of Income Tax [Line Items]
After-tax non-cash charge		70
Atlantic City Electric Co [Member]
Schedule Of Income Tax [Line Items]
Consolidated effective tax rates from continuing operations	36.40%		39.10%	5.90%	33.30%
State income taxes, net of Federal effect	1		1	1	1
After-tax effect of revised lease rerun		377
Additional interest income		6
Atlantic City Electric Co [Member] | Interest Expense [Member]
Schedule Of Income Tax [Line Items]
After-tax non-cash charge		$ 70