Commitments And Contingencies (Tax Legislation, Guarantees, Indemnifications, And Performance Contracts) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012
Commitments And Contingencies [Line Items]
Value of guarantees on both completed projects and projects under construction	$ 439
Value of performance contracts issued	15
Guarantee on obligations under construction contracts	$ 147
Performance Contracts Associated With Savings Guarantees [Member] | Pepco Energy Services [Member]
Commitments And Contingencies [Line Items]
Contract life, maximum remaining term	15 years
Performance Guarantee Contracts Associated With Production At Heat And Power Facilities [Member] | Pepco Energy Services [Member]
Commitments And Contingencies [Line Items]
Contract life, maximum remaining term	20 years