Commitments And Contingencies (Tax Legislation, Guarantees, Indemnifications, And Performance Contracts) (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Commitment And Contingencies [Line Items]
New accounting standards effect on pre-tax earnings		$ 7
New accounting standards effect on after-tax earnings		5
Value of guarantees on both completed projects and projects under construction	446
Value of guarantees under construction projects	15
Dividend declared on common stock, per share	$ 0.27
Contractual obligations due in, 2013	355
Contractual obligations due in, 2014 to 2015	707
Contractual obligations due in, 2016 to 2017	653
Contractual obligations due in, 2018 and thereafter	1,911
Energy Savings Or Combined Heat And Power Performance [Member]
Commitment And Contingencies [Line Items]
Accrued liability on contracts	1
Pepco Energy Services [Member] | Performance Contracts Associated With Savings Guarantees [Member]
Commitment And Contingencies [Line Items]
Contract life, maximum remaining term	13
Pepco Energy Services [Member] | Energy Savings Or Combined Heat And Power Performance [Member]
Commitment And Contingencies [Line Items]
Contract life, maximum remaining term	20
Delmarva Power & Light Co/De [Member]
Commitment And Contingencies [Line Items]
Contractual obligations due in, 2013	62
Contractual obligations due in, 2014 to 2015	126
Contractual obligations due in, 2016 to 2017	127
Contractual obligations due in, 2018 and thereafter	$ 293