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Summary of Significant Accounting Policies (Changes in the Liability for Transmission and Distribution Asset Removal Costs) (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Overview and Summary of Significant Accounting Policies [Abstract]    
Balance at January 1 $ 115.0dpl_EstimatedRemovalCosts $ 112.1dpl_EstimatedRemovalCosts
Additions 19.6dpl_EstimatedRemovalCostsAdditions 22.0dpl_EstimatedRemovalCostsAdditions
Settlements (15.3)dpl_EstimatedRemovalCostsSettlements (19.1)dpl_EstimatedRemovalCostsSettlements
Balance at December 31 $ 119.3dpl_EstimatedRemovalCosts $ 115.0dpl_EstimatedRemovalCosts