Derivative Instruments and Hedging Activities (Outstanding Derivative Instruments) (Details) - MWh	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights	3,800	10,200
Sale of Units Derivative Instruments Financial Transmission Rights	(1,500)	0
Derivative, Nonmonetary Notional Amount MWh	2,300	10,200
Not Designated as Hedging Instrument [Member] | Natural Gas [Member]
Purchase of Units Derivative Instruments Natural Gas	2,797,500
Sale of Units Derivative Instruments Natural Gas	0
Derivative, Nonmonetary Notional Amount, Energy Measure	2,797,500
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	4,016,600	5,049,900
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(6,012,300)	(1,663,000)
Derivative, Nonmonetary Notional Amount MWh	(1,995,700)	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	3,800	10,200
Sale of Units Derivative Instruments Financial Transmission Rights	(1,500)	0
Derivative, Nonmonetary Notional Amount MWh	2,300	10,200
Not Designated as Hedging Instrument [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Purchase of Units Derivative Instruments Natural Gas	2,797,500
Sale of Units Derivative Instruments Natural Gas	0
Derivative, Nonmonetary Notional Amount, Energy Measure	2,797,500
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	4,016,600	5,049,900
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(6,057,600)	(1,665,700)
Derivative, Nonmonetary Notional Amount MWh	(2,041,000)	3,384,200
Designated as Hedging Instrument [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	845,500	1,676,700
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(8,554,200)	(7,795,800)
Derivative, Nonmonetary Notional Amount MWh	(7,708,700)	(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	845,500	1,676,700
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(8,554,200)	(7,795,800)
Derivative, Nonmonetary Notional Amount MWh	(7,708,700)	(6,119,100)