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Derivative Instruments and Hedging Activities (Credit Risk-Related Contingent Features) (Details) - DPL Subsidiary - USD ($)
Dec. 31, 2015
Dec. 31, 2014
Credit Risk-Related Contingent Features [Line Items]    
Net liability position, derivative transactions $ 28,000,000 $ 12,000,000
Collateral posted for derivative transactions 8,000,000 5,000,000
Additional collateral that could have been required $ 2,000,000 $ 1,000,000