Income Taxes (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Schedule Of Income Tax [Line Items]
Consolidated effective tax rates from continuing operations	(45.80%)	14.90%
Change in estimates and interest related to uncertain and effectively settled tax positions	$ 67	$ (13)
Cross-border energy lease investments	64	(1)
Establishment of valuation allowance on deferred tax assets	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	8.00%	(26.30%)
Change in estimates and interest related to uncertain and effectively settled tax positions	(5)	(10)
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	38.10%	40.00%
Change in estimates and interest related to uncertain and effectively settled tax positions	(1)
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	(50.30%)	(100.00%)
After-tax effect of revised lease rerun	377
Additional interest income	6
Interest benefit related to uncertain and effectively settled tax positions	6
Atlantic City Electric Co [Member] | Interest Expense [Member]
Schedule Of Income Tax [Line Items]
After-tax non-cash charge	$ 70