Supplemental Financial Information (Reclassification out of ACOI) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended																			9 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Available-for-sale Securities [Member]	Mar. 31, 2013 Available-for-sale Securities [Member]	Mar. 31, 2014 Derivative [Member]	Mar. 31, 2013 Derivative [Member]	Mar. 31, 2013 Other Pension Plan, Defined Benefit [Member]	Mar. 31, 2014 Other Income [Member] Available-for-sale Securities [Member]	Mar. 31, 2013 Other Income [Member] Available-for-sale Securities [Member]	Mar. 31, 2014 Interest Expense [Member] Derivative [Member]	Mar. 31, 2014 Revenue [Member] Derivative [Member]	Mar. 31, 2013 Revenue [Member] Derivative [Member]	Mar. 31, 2014 Purchased Power [Member] Derivative [Member]	Mar. 31, 2013 Purchased Power [Member] Derivative [Member]	Mar. 31, 2014 DP&L [Member]	Mar. 31, 2013 DP&L [Member]	Mar. 31, 2014 DP&L [Member] Available-for-sale Securities [Member]	Mar. 31, 2013 DP&L [Member] Available-for-sale Securities [Member]	Mar. 31, 2014 DP&L [Member] Derivative [Member]	Sep. 30, 2013 DP&L [Member] Derivative [Member]	Mar. 31, 2014 DP&L [Member] Other Pension Plan, Defined Benefit [Member]	Mar. 31, 2014 DP&L [Member] Other Income [Member] Available-for-sale Securities [Member]	Mar. 31, 2013 DP&L [Member] Other Income [Member] Available-for-sale Securities [Member]	Mar. 31, 2014 DP&L [Member] Interest Expense [Member] Derivative [Member]	Mar. 31, 2013 DP&L [Member] Interest Expense [Member] Derivative [Member]	Mar. 31, 2014 DP&L [Member] Revenue [Member] Derivative [Member]	Mar. 31, 2013 DP&L [Member] Revenue [Member] Derivative [Member]	Mar. 31, 2014 DP&L [Member] Purchased Power [Member] Derivative [Member]	Mar. 31, 2013 DP&L [Member] Purchased Power [Member] Derivative [Member]
Other Comprehensive Income (Loss) - Financial Instruments Reclassfication			$ 0.3	$ 0.1				$ 0.3	$ 0.1								$ 0.3	$ 0.2				$ 0.3	$ 0.2
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(0.1)		(0.1)												(0.1)	(0.1)
Reclassification to earnings of available-for-sale securities, net of income tax expense/(benefit)	(0.2)	(0.1)	0.2	0.1											0.2	0.1
Other Comprehensive Income (Loss) - Cash Flow Hedge Reclassfications					8.6	0.3				(0.5)	10.2	(0.5)	(1.1)	0.8					8.9					(0.3)	(0.6)	(1.0)	(0.5)	10.2	1.1
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(3.1)	(0.1)			(3.1)	(0.1)									(3.2)	(0.2)
Reclassification of earnings of Cash Flow Hedge	(5.5)	(0.2)			5.5	0.2									5.7	(0.2)
Other Comprehensive Income (Loss) - Pension Reclassifications																					1.0
Other Comprehensive Income (Loss),Net Gain (Loss) Reclassification		(0.3)					0.3														0.6
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity		(0.3)					0.3														(0.4)
Reclassification to earnings of Pension		(0.3)					0.3														0.6
Total Reclassifications out of AOCI	$ 5.7	$ 0.6	$ 0.2		$ 5.5										$ 6.5	$ (0.1)	$ 0.2			$ 5.7	$ 0.6