Derivative Instruments and Hedging Activities (Outstanding Derivative Instruments) (Details) (USD $)	9 Months Ended
	Sep. 30, 2011 MWH		Dec. 31, 2010 MWH
FTRs [Member] | MTM position [Member]
Purchase of Units Derivative Instruments Financial Transmission Rights	11,300	[1]	9,000	[2]
Sales of Units Derivative Instruments Financial Transmission Rights	1,000	[1]		[2]
Derivative, Nonmonetary Notional Amount	12,300	[1]	9,000	[2]
Heating Oil [Member] | MTM position [Member]
Purchase of Volume Units Derivative Instruments Heating Oil Futures	3,654,000	[1]	6,216,000	[2]
Sales of Volume Units Derivative Instruments Heating Oil Futures				[2]
Derivative, Nonmonetary Notional Amount	3,654,000	[1]	6,216,000	[2]
DPL [Member] | Forward Power Contracts [Member] | MTM position [Member]
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(1,350,100)	[3]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	1,365,200	[3]
Derivative, Nonmonetary Notional Amount	15,100	[3]
Forward Power Contracts [Member] | MTM position [Member]
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(570,700)	[1]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged	587,000	[1]	195,600	[2]
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged			(108,500)	[2]
Derivative, Nonmonetary Notional Amount	16,300	[1]	87,100	[2]
Forward Power Contracts [Member] | Cash Flow Hedge [Member]
Purchase of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	974,900	[1]
Sales of Units Derivative Instruments Forward Power Contracts Designated as Cash Flow Hedge	(746,500)	[1]
Purchase of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged			580,800	[2]
Sales of Units Derivative Instruments Forward Power Contracts Not Designated as Hedged			(572,900)	[2]
Derivative, Nonmonetary Notional Amount	228,400	[1]	7,900	[2]
NYMEX Coal [Member] | MTM position [Member]
Purchase of Volume Units Derivative Instruments Coal Contracts	2,658,300	[1],[2]	4,006,800	[2],[4]
Sales of Volume Units Derivative Instruments Coal Contracts				[2],[4]
Derivative, Nonmonetary Notional Amount	2,658,300	[1],[2]	4,006,800	[2],[4]
Interest Rate Swap [Member] | Cash Flow Hedge [Member]
Purchase of Derivative Instruments Interest Rate Swaps	160,000,000	[3]	360,000,000
Sales of Derivative Instruments Interest Rate Swaps
Notional Amount of Derivatives	160,000,000	[3]	360,000,000

[1] Reflected in both DPL's and DP&L's Condensed Consolidated Financial Statements.

[2] *Includes our partners' share for the jointly-owned plants that DP&L operates.

[3] Reflected in only DPL's Condensed Consolidated Financial Statements.

[4] Includes our partners' share for the jointly-owned plants that DP&L operates.