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Contractual Obligations, Commercial Commitments and Contingencies (Narrative) (Details) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2016
Dec. 31, 2015
Public Utility, Property, Plant and Equipment [Line Items]    
Due to third parties, current $ 4.8 $ 0.5
THE DAYTON POWER AND LIGHT COMPANY [Member]    
Public Utility, Property, Plant and Equipment [Line Items]    
Debt maturity, earliest 2018  
Debt maturity, latest 2040  
DPLE [Member]    
Public Utility, Property, Plant and Equipment [Line Items]    
Third party guarantees $ 16.6  
Debt Obligation on 4.9% Equity Ownership [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]    
Public Utility, Property, Plant and Equipment [Line Items]    
Equity ownership interest 4.90%  
Equity ownership interest aggregate cost $ 74.9  
Electric Generation Company [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]    
Public Utility, Property, Plant and Equipment [Line Items]    
Debt obligation $ 1,528.0