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Commitments and Contingencies - Schedule of Commitments and Obligations (Parenthetical) (Detail) (USD $)
In Millions, unless otherwise specified
6 Months Ended
Jun. 30, 2013
Commitments And Contingencies [Line Items]  
Derivative portfolio guarantee $ 13
Obligations under guarantee 13
Leased equipment and fleet vehicles [Member]
 
Commitments And Contingencies [Line Items]  
Fair value of leased equipment and vehicles 0
Minimum [Member]
 
Commitments And Contingencies [Line Items]  
Lease term range 1 to 4 years
Maximum [Member]
 
Commitments And Contingencies [Line Items]  
Lease term range 3 to 8 years
PHI [Member]
 
Commitments And Contingencies [Line Items]  
Obligations under guarantee 55
Potomac Electric Power Co [Member]
 
Commitments And Contingencies [Line Items]  
Obligations under guarantee 8
Delmarva Power & Light Co/De [Member]
 
Commitments And Contingencies [Line Items]  
Obligations under guarantee 15
Atlantic City Electric Co [Member]
 
Commitments And Contingencies [Line Items]  
Obligations under guarantee $ 19