Stock-Based Compensation, Dividend Restrictions, and Calculations of Earnings Per Share of Common Stock - Dividends Received From Subsidiaries (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Dividends received from subsidiaries	$ 136	$ 70	$ 85
Potomac Electric Power Co [Member]
Dividends received from subsidiaries	46	35	25
Delmarva Power & Light Co/De [Member]
Dividends received from subsidiaries	30		60
Atlantic City Electric Co [Member]
Dividends received from subsidiaries	$ 60	$ 35