Derivative Instruments and Hedging Activities (Outstanding Derivative Instruments) (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2015 MWh gal	Dec. 31, 2014 MWh MMBTU gal
THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Derivative, Nonmonetary Notional Amount, Energy Measure		200,000
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights	24,200	10,500
Derivative, Nonmonetary Notional Amount MWh	24,200	10,500
Not Designated as Hedging Instrument [Member] | Commodity Contract - Heating Oil [Member]
Purchase of Volume Units Derivative Instruments Heating Oil Futures | gal	168,000	378,000
Derivative, Nonmonetary Notional Amount, Volume | gal	168,000	378,000
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	3,621,900	1,725,200
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(3,530,400)	(2,707,800)
Derivative, Nonmonetary Notional Amount MWh	91,500	(982,600)
Not Designated as Hedging Instrument [Member] | Natural Gas [Member]
Derivative, Nonmonetary Notional Amount, Energy Measure		200,000
Not Designated as Hedging Instrument [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights	24,200	10,500
Derivative, Nonmonetary Notional Amount MWh	24,200	10,500
Not Designated as Hedging Instrument [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Purchase of Volume Units Derivative Instruments Heating Oil Futures | gal	168,000	378,000
Derivative, Nonmonetary Notional Amount, Volume | gal	168,000	378,000
Not Designated as Hedging Instrument [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	3,621,900	1,725,200
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(3,606,800)	(2,804,000)
Derivative, Nonmonetary Notional Amount MWh	15,100	(1,078,800)
Designated as Hedging Instrument [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	1,723,400	175,000
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(8,809,400)	(2,991,000)
Derivative, Nonmonetary Notional Amount MWh	(7,086,000)	(2,816,000)
Designated as Hedging Instrument [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	1,723,400	175,000
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(8,809,400)	(2,991,000)
Derivative, Nonmonetary Notional Amount MWh	(7,086,000)	(2,816,000)