Derivative Instruments and Hedging Activities (Outstanding Derivative Instruments) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
FTRs [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights	2,800	7,100
Sales of Units Derivative Instruments Financial Transmission Rights		(700)
Derivative, Nonmonetary Notional Amount	2,800	6,400
FTRs [Member] | DP&L [Member] | MTM position [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights	2,800	7,100
Sales of Units Derivative Instruments Financial Transmission Rights		(700)
Derivative, Nonmonetary Notional Amount	2,800	6,400
Heating Oil [Member]
Purchase of Volume Units Derivative Instruments Heating Oil Futures	1,680,000	2,772,000
Derivative, Nonmonetary Notional Amount	1,680,000	2,772,000
Heating Oil [Member] | DP&L [Member] | MTM position [Member]
Purchase of Volume Units Derivative Instruments Heating Oil Futures	1,680,000	2,772,000
Derivative, Nonmonetary Notional Amount	1,680,000	2,772,000
Forward Power Contracts [Member] | MTM position [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	1,195,400	1,769,400
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(1,213,500)	(1,739,500)
Derivative, Nonmonetary Notional Amount	(18,100)	29,900
Forward Power Contracts [Member] | Cash Flow Hedge [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	881,100	886,200
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(107,200)	(341,600)
Derivative, Nonmonetary Notional Amount	773,900	544,600
Forward Power Contracts [Member] | DP&L [Member] | MTM position [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	618,700	525,100
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	(618,700)	(525,100)
Forward Power Contracts [Member] | DP&L [Member] | Cash Flow Hedge [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	881,000	886,200
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(107,200)	(341,600)
Derivative, Nonmonetary Notional Amount	773,800	544,600
NYMEX Coal [Member]
Purchase of Volume Units Derivative Instruments Coal Contracts	1,410,500	2,015,000
Derivative, Nonmonetary Notional Amount	1,410,500	2,015,000
NYMEX Coal [Member] | DP&L [Member] | MTM position [Member]
Purchase of Volume Units Derivative Instruments Coal Contracts	1,410,500	2,015,000
Derivative, Nonmonetary Notional Amount	1,410,500	2,015,000
Interest Rate Swap [Member]
Purchase of Derivative Instruments Interest Rate Swaps	160,000,000	160,000,000
Notional Amount of Derivatives	160,000,000	160,000,000