Derivative Instruments and Hedging Activities (Outstanding Derivative Instruments) (Details)	12 Months Ended
	Dec. 31, 2014 MWh gal	Dec. 31, 2015 MWh
Designated as Hedging Instrument [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	175,000	1,676,700
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(2,991,000)	(7,795,800)
Derivative, Nonmonetary Notional Amount MWh	(2,816,000)	(6,119,100)
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	175,000	1,676,700
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(2,991,000)	(7,795,800)
Derivative, Nonmonetary Notional Amount MWh	(2,816,000)	(6,119,100)
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights	10,500	10,200
Sale of Units Derivative Instruments Financial Transmission Rights	0	0
Derivative, Nonmonetary Notional Amount MWh	10,500	10,200
Not Designated as Hedging Instrument [Member] | Commodity Contract - Heating Oil [Member]
Purchase of Volume Units Derivative Instruments Heating Oil Futures | gal	378,000
Sale of Volume Units Derivative Instruments Heating Oil Futures | gal	0
Derivative, Nonmonetary Notional Amount, Volume | gal	378,000
Not Designated as Hedging Instrument [Member] | Natural Gas [Member]
Purchase of Units Derivative Instruments Natural Gas	200,000
Sale of Units Derivative Instruments Natural Gas	0
Derivative, Nonmonetary Notional Amount,Natural Gas	200,000
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	1,725,200	5,049,900
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(2,707,800)	(1,663,000)
Derivative, Nonmonetary Notional Amount MWh	(982,600)	3,386,900
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	10,500	10,200
Sale of Units Derivative Instruments Financial Transmission Rights	0	0
Derivative, Nonmonetary Notional Amount MWh	10,500	10,200
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	378,000
Sale of Volume Units Derivative Instruments Heating Oil Futures | gal	0
Derivative, Nonmonetary Notional Amount, Volume | gal	378,000
Not Designated as Hedging Instrument [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Purchase of Units Derivative Instruments Natural Gas	200,000
Derivative, Nonmonetary Notional Amount,Natural Gas	200,000
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	1,725,200	5,049,900
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(2,804,000)	(1,665,700)
Derivative, Nonmonetary Notional Amount MWh	(1,078,800)	3,384,200