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Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2011
Significant Accounting Policies [Abstract]  
Annual Depreciation Rates
   Transmission and
Distribution		    
Generation		  
     2011     2010     2009     2011     2010     2009  

Pepco

      2.6 %      2.6 %      2.7 %      —          —          —     

DPL

      2.8 %      2.8 %      2.8 %      —          —          —     

ACE

      3.0 %      2.8 %      2.8 %      —          —          —     

Pepco Energy Services (a)

      —          —          —          10.2 %     16.9 %      11.4 % 

 

(a) Percentages reflect accelerated depreciation of the Benning Road and Buzzard Point generating plants scheduled for retirement in May 2012.