Supplemental Financial Information (Reclassification out of ACOI) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended			3 Months Ended	9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		6 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Available-for-sale Securities [Member]	Sep. 30, 2013 Available-for-sale Securities [Member]	Sep. 30, 2013 Derivative [Member]	Sep. 30, 2013 Derivative [Member]	Sep. 30, 2012 Derivative [Member]	Sep. 30, 2013 Other Pension Plans, Defined Benefit [Member]	Sep. 30, 2013 Other Income [Member] Available-for-sale Securities [Member]	Sep. 30, 2013 Other Income [Member] Available-for-sale Securities [Member]	Sep. 30, 2012 Other Income [Member] Other Pension Plans, Defined Benefit [Member]	Sep. 30, 2012 Interest Expense [Member] Derivative [Member]	Sep. 30, 2013 Revenue [Member] Derivative [Member]	Sep. 30, 2012 Revenue [Member] Derivative [Member]	Sep. 30, 2013 Revenue [Member] Derivative [Member]	Sep. 30, 2012 Revenue [Member] Derivative [Member]	Sep. 30, 2013 Purchased Power [Member] Derivative [Member]	Sep. 30, 2012 Purchased Power [Member] Derivative [Member]	Sep. 30, 2013 Purchased Power [Member] Derivative [Member]	Sep. 30, 2012 Purchased Power [Member] Derivative [Member]	Sep. 30, 2013 DP&L [Member]	Sep. 30, 2012 DP&L [Member]	Jun. 30, 2012 DP&L [Member]	Sep. 30, 2013 DP&L [Member]	Sep. 30, 2013 DP&L [Member] Available-for-sale Securities [Member]	Sep. 30, 2013 DP&L [Member] Available-for-sale Securities [Member]	Sep. 30, 2013 DP&L [Member] Derivative [Member]	Sep. 30, 2012 DP&L [Member] Derivative [Member]	Jun. 30, 2012 DP&L [Member] Derivative [Member]	Sep. 30, 2013 DP&L [Member] Derivative [Member]	Sep. 30, 2013 DP&L [Member] Other Pension Plans, Defined Benefit [Member]	Sep. 30, 2012 DP&L [Member] Other Pension Plans, Defined Benefit [Member]	Jun. 30, 2012 DP&L [Member] Other Pension Plans, Defined Benefit [Member]	Sep. 30, 2013 DP&L [Member] Other Pension Plans, Defined Benefit [Member]	Sep. 30, 2013 DP&L [Member] Other Income [Member] Available-for-sale Securities [Member]	Sep. 30, 2013 DP&L [Member] Other Income [Member] Available-for-sale Securities [Member]	Sep. 30, 2013 DP&L [Member] Interest Expense [Member] Derivative [Member]	Sep. 30, 2012 DP&L [Member] Interest Expense [Member] Derivative [Member]	Jun. 30, 2012 DP&L [Member] Interest Expense [Member] Derivative [Member]	Sep. 30, 2013 DP&L [Member] Interest Expense [Member] Derivative [Member]	Sep. 30, 2013 DP&L [Member] Revenue [Member] Derivative [Member]	Sep. 30, 2012 DP&L [Member] Revenue [Member] Derivative [Member]	Jun. 30, 2012 DP&L [Member] Revenue [Member] Derivative [Member]	Sep. 30, 2013 DP&L [Member] Revenue [Member] Derivative [Member]	Sep. 30, 2013 DP&L [Member] Purchased Power [Member] Derivative [Member]	Jun. 30, 2012 DP&L [Member] Purchased Power [Member] Derivative [Member]	Sep. 30, 2013 DP&L [Member] Purchased Power [Member] Derivative [Member]
Other Comprehensive Income (Loss) - Financial Instruments Reclassfication				$ 0.6	$ 2.1					$ 0.6	$ 2.1															$ 0.6	$ 2.1									$ 0.6	$ 2.1
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(0.2)	(0.7)		(0.2)	(0.7)								0.2	0.5	0.1	2.2	(1.7)					(0.2)			(0.7)
Reclassification to earnings of available-for-sale securities, net of income tax expense/(benefit)	0.4	1.4		0.4	1.4																	0.4			1.4
Other Comprehensive Income (Loss) - Cash Flow Hedge Reclassfications						2.1	5.1	(1.6)										1.6	(0.1)	2.9	(0.1)							1.8	(0.8)	(3.8)	4.5							(0.6)	(0.6)	(1.8)	(1.8)	0.4	(0.2)	(2.2)	2.1	2.0	0.2	4.2
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(0.8)	(2.1)	0.7			(0.8)	(2.1)	0.8														(0.8)	0.1	0.7	(2.2)
Reclassification of earnings of Cash Flow Hedge	1.3	3.0	(0.8)			1.3	3.0	(0.8)														1.0	(0.7)	(3.1)	2.3
Other Comprehensive Income (Loss) - Pension Reclassifications												(0.1)																				1.4	1.6	4.6	4.2
Other Comprehensive Income (Loss),Net Gain (Loss) Reclassification		0.3	(0.1)						0.3																							0.9	1.0	3.0	2.7
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity		0.3							0.3																							(0.5)	(0.6)	(1.6)	(1.5)
Reclassification to earnings of Pension		0.3	(0.1)						0.3																							0.9	1.0	3.0	2.7
Total Reclassifications out of AOCI	$ 1.7	$ 4.7	$ (0.8)		$ 1.4		$ 3.0		$ 0.3													$ 2.3	$ 0.3	$ (0.1)	$ 6.4		$ 1.4				$ 2.3				$ 2.7