Derivative Instruments and Hedging Activities (Outstanding Derivative Instruments) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 MWh	Dec. 31, 2011 MWh
FTRs [Member] | MTM position [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights	6,900	7,100
Sales of Units Derivative Instruments Financial Transmission Rights		(700)
Derivative, Nonmonetary Notional Amount MWh	6,900	6,400
FTRs [Member] | DP&L [Member] | MTM position [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights	6,900	7,100
Sales of Units Derivative Instruments Financial Transmission Rights		(700)
Derivative, Nonmonetary Notional Amount MWh	6,900	6,400
Heating Oil [Member] | MTM position [Member]
Purchase of Volume Units Derivative Instruments Heating Oil Futures	1,764,000	2,772,000
Derivative, Nonmonetary Notional Amount Volume	1,764,000	2,772,000
Heating Oil [Member] | DP&L [Member] | MTM position [Member]
Purchase of Volume Units Derivative Instruments Heating Oil Futures	1,764,000	2,772,000
Derivative, Nonmonetary Notional Amount Volume	1,764,000	2,772,000
Forward Power Contracts [Member] | MTM position [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	2,510,700	1,769,400
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(4,760,400)	(1,739,500)
Derivative, Nonmonetary Notional Amount MWh	(2,249,700)	29,900
Forward Power Contracts [Member] | Cash Flow Hedge [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	1,021,000	886,200
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(2,197,900)	(341,600)
Derivative, Nonmonetary Notional Amount MWh	(1,176,900)	544,600
Forward Power Contracts [Member] | DP&L [Member] | MTM position [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	2,296,600	525,100
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(4,760,400)	(525,100)
Derivative, Nonmonetary Notional Amount MWh	(2,463,800)
Forward Power Contracts [Member] | DP&L [Member] | Cash Flow Hedge [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	1,021,000	886,200
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(2,197,900)	(341,600)
Derivative, Nonmonetary Notional Amount MWh	(1,176,900)	544,600
NYMEX Coal [Member] | MTM position [Member]
Purchase of Volume Units Derivative Instruments Coal Contracts		2,015,000
Derivative, Nonmonetary Notional Amount Mass		2,015,000
NYMEX Coal [Member] | DP&L [Member] | MTM position [Member]
Purchase of Volume Units Derivative Instruments Coal Contracts		2,015,000
Derivative, Nonmonetary Notional Amount Mass		2,015,000
Interest Rate Swap [Member] | Cash Flow Hedge [Member]
Purchase of Derivative Instruments Interest Rate Swaps	160,000,000	160,000,000
Notional Amount of Derivatives	160,000,000	160,000,000