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Commitments and Contingencies - Retained Environmental Exposures - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
1 Months Ended 12 Months Ended 1 Months Ended
Jul. 31, 2010
Dec. 31, 2012
Pepco Energy Services [Member]
Jul. 31, 2010
Conectiv Energy [Member]
Facility
Jul. 31, 2010
PHI [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
Number of facility locations     9