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Pension and Other Postretirement Benefits - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended 0 Months Ended 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2013
Other Postretirement Benefits [Member]
Dec. 31, 2012
Other Postretirement Benefits [Member]
Dec. 31, 2011
Other Postretirement Benefits [Member]
Dec. 31, 2013
Pension Benefits [Member]
Dec. 31, 2012
Pension Benefits [Member]
Dec. 31, 2011
Pension Benefits [Member]
Dec. 31, 2013
PHI Service Company [Member]
Retiree [Member]
Dec. 31, 2012
PHI Service Company [Member]
Retiree [Member]
Jul. 02, 2013
PHI Service Company [Member]
Other Postretirement Benefits [Member]
Dec. 31, 2013
PHI Service Company [Member]
Other Postretirement Benefits [Member]
Amendments
Dec. 31, 2012
PHI Service Company [Member]
Other Postretirement Benefits [Member]
Dec. 31, 2013
Delmarva Power & Light Co/De [Member]
Dec. 31, 2012
Delmarva Power & Light Co/De [Member]
Dec. 31, 2011
Delmarva Power & Light Co/De [Member]
Dec. 31, 2013
Delmarva Power & Light Co/De [Member]
Retiree [Member]
Dec. 31, 2012
Delmarva Power & Light Co/De [Member]
Retiree [Member]
Dec. 31, 2013
Delmarva Power & Light Co/De [Member]
Other Postretirement Benefits [Member]
Amendments
Dec. 31, 2012
Delmarva Power & Light Co/De [Member]
Other Postretirement Benefits [Member]
Dec. 31, 2011
Delmarva Power & Light Co/De [Member]
Other Postretirement Benefits [Member]
Dec. 31, 2013
Atlantic City Electric Co [Member]
Dec. 31, 2012
Atlantic City Electric Co [Member]
Dec. 31, 2011
Atlantic City Electric Co [Member]
Dec. 31, 2013
Atlantic City Electric Co [Member]
Retiree [Member]
Dec. 31, 2012
Atlantic City Electric Co [Member]
Retiree [Member]
Dec. 31, 2013
Atlantic City Electric Co [Member]
Other Postretirement Benefits [Member]
Amendments
Dec. 31, 2012
Atlantic City Electric Co [Member]
Other Postretirement Benefits [Member]
Dec. 31, 2011
Atlantic City Electric Co [Member]
Other Postretirement Benefits [Member]
Dec. 31, 2013
Subsidiaries [Member]
Dec. 31, 2012
Subsidiaries [Member]
Dec. 31, 2011
Subsidiaries [Member]
Dec. 31, 2013
Subsidiaries [Member]
Other Postretirement Benefits [Member]
Dec. 31, 2012
Subsidiaries [Member]
Other Postretirement Benefits [Member]
Dec. 31, 2013
Potomac Electric Power Co [Member]
Dec. 31, 2012
Potomac Electric Power Co [Member]
Dec. 31, 2011
Potomac Electric Power Co [Member]
Dec. 31, 2013
Potomac Electric Power Co [Member]
Other Postretirement Benefits [Member]
Amendments
Dec. 31, 2012
Potomac Electric Power Co [Member]
Other Postretirement Benefits [Member]
Dec. 31, 2011
Potomac Electric Power Co [Member]
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]                                                                                  
Accumulated benefit obligation $ 2,100 $ 2,300   $ 574 $ 775 $ 750 $ 2,238 $ 2,494 $ 2,124                                                                
Net loss to be amortized from AOCL or regulatory assets into net periodic benefit cost       6     44                                                                    
Prior service cost to be amortized from AOCL or regulatory assets into net periodic benefit cost       (124)     3                                                                    
Service periods for participating employee 11 years 11 years                                                                              
Number of amendments, PHI approved                         2             2               2                     2    
Reduction of the projected benefit obligation       (124)     3           193                                                        
Prior service credit included in projected benefit obligation                         124                                                        
Amortization period                         10 years                                                        
Net periodic benefit cost                         17 69 3               2                         4          
Change in the discount rate                       4.95%   4.10%                                                      
Percentage of postretirement benefit costs                         37.00%             29.00%               42.00%                     38.00%    
Percentage of plan asset target allocation 66.00%                                                                                
Unfunded capital commitments 12 15                                                                              
Pension contributions 120 200 110             80 85       10 85 40 10 85       30 30 30 30 30                 0 85 40      
OPEB contributions       6 5                             3 7 6           6 7 7       7 13       6 5 7
Medicare Part D subsidy receipts 0 4                                                                              
Percentage of participants vested 100.00%                                                                                
Defined contribution plan matching contributions 12 12 11                                                                            
Pension and other postretirement net periodic benefit cost                             18 23 23           17 24 21                     34 39 43      
Prepaid pension expense                             228 232             106 88                       332 353        
Other postretirement benefit obligations 206 454   206 454                     23 22             35 34                       61 66        
Net periodic benefit cost $ 95 $ 110 $ 94 $ 18 $ 35 $ 33 $ 77 $ 75 $ 61           $ 18 $ 23 $ 23     $ 3     $ 17 $ 24 $ 21     $ 2     $ 26 $ 24 $ 7     $ 34 $ 39 $ 43 $ 4