Commitments and Contingencies - Tax Legislation, Guarantees, Indemnifications, and Performance Contracts - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended			0 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jan. 23, 2014 Subsequent Event [Member]	Dec. 31, 2013 Energy Savings or Combined Heat and Power Performance [Member]	Dec. 31, 2013 Pepco Energy Services [Member] Completed Performance Contracts Associated With Savings Guarantees [Member]	Dec. 31, 2013 Pepco Energy Services [Member] Uncompleted Performance Contracts Associated With Savings Guarantees [Member]	Dec. 31, 2013 Pepco Energy Services [Member] Energy Savings or Combined Heat and Power Performance [Member]	Dec. 31, 2013 Delmarva Power & Light Co/De [Member]	Dec. 31, 2012 Delmarva Power & Light Co/De [Member]	Dec. 31, 2011 Delmarva Power & Light Co/De [Member]	Dec. 31, 2013 Atlantic City Electric Co [Member]	Dec. 31, 2012 Atlantic City Electric Co [Member]	Dec. 31, 2011 Atlantic City Electric Co [Member]	Dec. 31, 2013 Potomac Electric Power Co [Member]	Dec. 31, 2012 Potomac Electric Power Co [Member]	Dec. 31, 2011 Potomac Electric Power Co [Member]
Commitment and Contingencies [Line Items]
Value of guarantees completed projects						$ 252
Contract life, maximum remaining term						12 years		20 years
Value of guarantees on projects under construction							187
Maximum term of project under construction							23 years
Value of guarantees under construction projects								15
Accrued liability on contracts					1
Dividend declared on common stock, per share				$ 27
Dividend declared, payable date				Mar. 31, 2014
Dividends payable, date of record				Mar. 10, 2014
Contractual obligations due in, 2014	278								64			214
Contractual obligations due in, 2015 to 2016	562								131			431
Contractual obligations due in, 2017 to 2018	486								131			355
Contractual obligations due in, 2019 and thereafter	1,386								300			1,086
Rental expense for operating leases	54	52	46						13	12	11	12	11	10	7	6	4
Future minimum operating lease payments, 2014	44								13			5			6
Future minimum operating lease payments, 2015	42								13			5			6
Future minimum operating lease payments, 2016	39								11			5			6
Future minimum operating lease payments, 2017	36								10			4			5
Future minimum operating lease payments, 2018	37								14			4			4
Future minimum operating lease payments, thereafter	342								111			29			21
Ownership interest									11.90%
Present value of future minimum lease payments									$ 84