Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2013
Schedule of Income Tax [Line Items]
Change in estimates and interest related to uncertain tax positions	$ 51
Establishment of valuation allowance on deferred tax assets	101
PCI future deferred tax asset	101	101
After-tax effect of revised lease rerun	377
Potomac Electric Power Co [Member]
Schedule of Income Tax [Line Items]
After-tax non-cash charge	54
Additional interest income	5
After-tax effect of revised lease rerun	377
Delmarva Power & Light Co/De [Member]
Schedule of Income Tax [Line Items]
After-tax non-cash charge	54
Additional interest income	1
After-tax effect of revised lease rerun	377
Atlantic City Electric Co [Member]
Schedule of Income Tax [Line Items]
After-tax non-cash charge	54
Additional interest income	6
After-tax effect of revised lease rerun	$ 377