Derivative Instruments and Hedging Activities (Outstanding Derivative Instruments) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013 MWh	Dec. 31, 2012 MWh
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member]
Purchase of Derivative Instruments Interest Rate Swaps	160,000,000	160,000,000
Notional Amount of Derivatives	160,000,000	160,000,000
Designated as Hedging Instrument [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	842,600	1,021,000
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(2,040,900)	(2,197,900)
Derivative, Nonmonetary Notional Amount MWh	(1,198,300)	(1,176,900)
Designated as Hedging Instrument [Member] | DP&L [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	842,600	1,021,000
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(2,040,900)	(2,197,900)
Derivative, Nonmonetary Notional Amount MWh	(1,198,300)	(1,176,900)
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights	2,800	6,900
Derivative, Nonmonetary Notional Amount MWh	2,800	6,900
Not Designated as Hedging Instrument [Member] | Commodity Contract - Heating Oil [Member]
Purchase of Volume Units Derivative Instruments Heating Oil Futures	1,890,000	1,764,000
Derivative, Nonmonetary Notional Amount Volume	1,890,000	1,764,000
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	2,221,400	2,510,700
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(7,069,800)	(4,760,400)
Derivative, Nonmonetary Notional Amount MWh	(4,848,400)	(2,249,700)
Not Designated as Hedging Instrument [Member] | DP&L [Member] | Commodity Contract - FTR [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights	2,800	6,900
Derivative, Nonmonetary Notional Amount MWh	2,800	6,900
Not Designated as Hedging Instrument [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Purchase of Volume Units Derivative Instruments Heating Oil Futures	1,890,000	1,764,000
Derivative, Nonmonetary Notional Amount Volume	1,890,000	1,764,000
Not Designated as Hedging Instrument [Member] | DP&L [Member] | Forward Contract Power [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	2,221,400	2,296,600
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(7,069,800)	(4,760,400)
Derivative, Nonmonetary Notional Amount MWh	(4,848,400)	(2,463,800)