Commitments And Contingencies (Retained Environmental Exposures) (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended			12 Months Ended
	Jul. 31, 2010	Jul. 31, 2010 Conectiv Energy [Member]	Jul. 31, 2010 PHI [Member]	Dec. 31, 2012 Pepco Energy Services [Member]
Commitment And Contingencies [Line Items]
Certain allegedly unauthorized charges				$ 7
Additional compounded interest				9
Environmental remediation expense minimum	7
Environmental remediation expense maximum	18
Third party maximum and seller floor for environmental remediation costs		$ 10	$ 10