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Segment Information - Additional Information (Detail)
9 Months Ended
Sep. 30, 2014
Segment
Potomac Electric Power Co [Member]
 
Sales Information [Line Items]  
Number of operating segment 1
Delmarva Power & Light Co/De [Member]
 
Sales Information [Line Items]  
Number of operating segment 1
Atlantic City Electric Co [Member]
 
Sales Information [Line Items]  
Number of operating segment 1