Derivative Instruments and Hedging Activities (Gains or Losses Recognized in AOCI for the Cash Flow Hedges) (Details) (USD $) In Millions	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended			6 Months Ended			3 Months Ended				6 Months Ended				3 Months Ended			6 Months Ended			3 Months Ended				6 Months Ended
	Jun. 30, 2011 DP&L [Member] Forward Contract Power [Member] Interest Expense [Member]	Jun. 30, 2010 DP&L [Member] Forward Contract Power [Member] Interest Expense [Member]	Jun. 30, 2011 DP&L [Member] Forward Contract Power [Member] Interest Expense [Member]	Jun. 30, 2010 DP&L [Member] Forward Contract Power [Member] Interest Expense [Member]	Jun. 30, 2011 DP&L [Member] Interest Expense [Member] Interest Rate Swap [Member]	Jun. 30, 2010 DP&L [Member] Interest Expense [Member] Interest Rate Swap [Member]	Jun. 30, 2011 DP&L [Member] Interest Expense [Member] Interest Rate Swap [Member]	Jun. 30, 2010 DP&L [Member] Interest Expense [Member] Interest Rate Swap [Member]	Jun. 30, 2011 Forward Contract Power [Member] Interest Expense [Member]	Jun. 30, 2010 Forward Contract Power [Member] Interest Expense [Member]	Jun. 30, 2011 Forward Contract Power [Member] Interest Expense [Member]	Jun. 30, 2010 Forward Contract Power [Member] Interest Expense [Member]	Jun. 30, 2011 Interest Expense [Member] Interest Rate Swap [Member]	Jun. 30, 2010 Interest Expense [Member] Interest Rate Swap [Member]	Jun. 30, 2011 Interest Expense [Member] Interest Rate Swap [Member]	Jun. 30, 2010 Interest Expense [Member] Interest Rate Swap [Member]	Jun. 30, 2011 DP&L [Member] Forward Contract Power [Member] Revenues [Member]	Jun. 30, 2010 DP&L [Member] Forward Contract Power [Member] Revenues [Member]	Jun. 30, 2011 DP&L [Member] Forward Contract Power [Member] Revenues [Member]	Jun. 30, 2010 DP&L [Member] Forward Contract Power [Member] Revenues [Member]	Jun. 30, 2011 DP&L [Member] Revenues [Member] Interest Rate Swap [Member]	Jun. 30, 2010 DP&L [Member] Revenues [Member] Interest Rate Swap [Member]	Jun. 30, 2011 DP&L [Member] Revenues [Member] Interest Rate Swap [Member]	Jun. 30, 2010 DP&L [Member] Revenues [Member] Interest Rate Swap [Member]	Jun. 30, 2011 Forward Contract Power [Member] Revenues [Member]	Jun. 30, 2010 Forward Contract Power [Member] Revenues [Member]	Jun. 30, 2011 Forward Contract Power [Member] Revenues [Member]	Jun. 30, 2010 Forward Contract Power [Member] Revenues [Member]	Jun. 30, 2011 Revenues [Member] Interest Rate Swap [Member]	Jun. 30, 2010 Revenues [Member] Interest Rate Swap [Member]	Jun. 30, 2011 Revenues [Member] Interest Rate Swap [Member]	Jun. 30, 2010 Revenues [Member] Interest Rate Swap [Member]	Jun. 30, 2011 DP&L [Member] Forward Contract Power [Member]		Jun. 30, 2010 DP&L [Member] Forward Contract Power [Member]	Jun. 30, 2011 DP&L [Member] Forward Contract Power [Member]		Jun. 30, 2010 DP&L [Member] Forward Contract Power [Member]	Jun. 30, 2011 Forward Contract Power [Member]		Jun. 30, 2010 Forward Contract Power [Member]		Jun. 30, 2011 Forward Contract Power [Member]		Jun. 30, 2010 Forward Contract Power [Member]		Jun. 30, 2011 DP&L [Member] Interest Rate Swap [Member]		Jun. 30, 2010 DP&L [Member] Interest Rate Swap [Member]	Jun. 30, 2011 DP&L [Member] Interest Rate Swap [Member]		Dec. 31, 2009 DP&L [Member] Interest Rate Swap [Member]	Jun. 30, 2011 Interest Rate Swap [Member]		Jun. 30, 2010 Interest Rate Swap [Member]		Jun. 30, 2011 Interest Rate Swap [Member]		Jun. 30, 2010 Interest Rate Swap [Member]
Beginning accumulated derivative gain / (loss) in AOCI																																	$ (1.6)		$ 3.6	$ (1.8)		$ (1.4)	$ (1.6)		$ 3.6		$ (1.8)		$ (1.4)		$ 11.6		$ 14.1	$ 12.2		$ 14.7	$ 22.4		$ 14.1		$ 21.4		$ 14.7
Net gains / (losses) associated with current period hedging transactions																																	(0.5)		(2.1)	(0.9)		(2.3)	(0.5)		(2.1)		(0.9)		(2.3)								(10.8)		(5.8)		(9.2)		(5.8)
Net gains reclassified to earnings					(0.6)	(0.6)	(1.2)	(1.2)					0.7	(0.6)	0.1	(1.2)	0.3	(1.5)	0.5	3.7					0.3	(1.5)	0.5	3.7															0.7
Ending accumulated derivative gain / (loss) in AOCI																																	(1.5)		0	(1.5)		0	(1.5)				(1.5)				11.0		13.5	11.0		14.7	12.3		7.7		12.3		7.7
Net gains / (losses) associated with the ineffective portion of the hedging transaction													(1.3)		(1.3)
Portion expected to be reclassified to earnings in the next twelve months																																	$ (1.9)	[1]		$ (1.9)	[1]		$ (1.9)	[1]		[1]	$ (1.9)	[1]		[1]	$ (2.4)	[1]		$ (2.4)	[1]		$ (2.4)	[1]		[1]	$ (2.4)	[1]		[1]
Maximum length of time that we are hedging our exposure to variability in future cash flows related to forecasted transactions (in months)																																	42			42			42				42				-			-			27				27

[1] The actual amounts that we reclassify from AOCI to earnings related to power can differ from the estimate above due to market price changes.