Supplemental Financial Information (Accumulated Other Comprehensive Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Total Reclassifications out of AOCI	$ 2.6		$ 3.2	$ (0.9)
Total Adjustments to AOCI			10.8
Other Comprehensive Income (Loss), Net of Tax	11.9	(13.5)	14.0	(6.4)
Accumulated Other Comprehensive Income (Loss), Net of Tax	10.1		10.1		(3.9)
DP&L [Member]
Total Reclassifications out of AOCI	2.3	(0.5)	2.2	(2.3)
Total Adjustments to AOCI			0.7
Other Comprehensive Income (Loss), Net of Tax			2.9
Accumulated Other Comprehensive Income (Loss), Net of Tax	(35.8)		(35.8)		(38.7)
Available-for-sale Securities [Member]
Total Reclassifications out of AOCI			1.1
Total Adjustments to AOCI			(1.6)
Other Comprehensive Income (Loss), Net of Tax			(0.5)
Accumulated Other Comprehensive Income (Loss), Net of Tax	(0.1)		(0.1)		0.4
Available-for-sale Securities [Member] | DP&L [Member]
Total Reclassifications out of AOCI			1.1
Total Adjustments to AOCI			(1.6)
Other Comprehensive Income (Loss), Net of Tax			(0.5)
Accumulated Other Comprehensive Income (Loss), Net of Tax	0.5		0.5		1.0
Derivative [Member]
Total Reclassifications out of AOCI			1.8
Total Adjustments to AOCI			12.4
Other Comprehensive Income (Loss), Net of Tax			14.2
Accumulated Other Comprehensive Income (Loss), Net of Tax	11.7		11.7		(2.5)
Derivative [Member] | DP&L [Member]
Total Reclassifications out of AOCI			1.1
Total Adjustments to AOCI			0.5
Other Comprehensive Income (Loss), Net of Tax			1.6
Accumulated Other Comprehensive Income (Loss), Net of Tax	4.2		4.2		2.6
Other Pension Plans, Defined Benefit [Member]
Total Reclassifications out of AOCI			0.3
Other Comprehensive Income (Loss), Net of Tax			0.3
Accumulated Other Comprehensive Income (Loss), Net of Tax	(1.5)		(1.5)		(1.8)
Other Pension Plans, Defined Benefit [Member] | DP&L [Member]
Total Adjustments to AOCI			1.8
Other Comprehensive Income (Loss), Net of Tax			1.8
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (40.5)		$ (40.5)		$ (42.3)