Supplemental Financial Information (Accumulated Other Comprehensive Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended			3 Months Ended		6 Months Ended	9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 DP&L [Member]	Sep. 30, 2012 DP&L [Member]	Jun. 30, 2012 DP&L [Member]	Sep. 30, 2013 DP&L [Member]	Dec. 31, 2012 DP&L [Member]	Sep. 30, 2013 Available-for-sale Securities [Member]	Dec. 31, 2012 Available-for-sale Securities [Member]	Sep. 30, 2013 Available-for-sale Securities [Member] DP&L [Member]	Dec. 31, 2012 Available-for-sale Securities [Member] DP&L [Member]	Sep. 30, 2013 Derivative [Member]	Dec. 31, 2012 Derivative [Member]	Sep. 30, 2013 Derivative [Member] DP&L [Member]	Dec. 31, 2012 Derivative [Member] DP&L [Member]	Sep. 30, 2013 Other Pension Plans, Defined Benefit [Member]	Dec. 31, 2012 Other Pension Plans, Defined Benefit [Member]	Sep. 30, 2013 Other Pension Plans, Defined Benefit [Member] DP&L [Member]	Dec. 31, 2012 Other Pension Plans, Defined Benefit [Member] DP&L [Member]
Total Reclassifications out of AOCI	$ 1.7		$ 4.7	$ (0.8)		$ 2.3	$ 0.3	$ (0.1)	$ 6.4		$ 1.4		$ 1.4		$ 3.0		$ 2.3		$ 0.3		$ 2.7
Total Adjustments to AOCI			17.4						(1.8)		(1.3)		(1.8)		18.7
Other Comprehensive Income (Loss), Net of Tax	8.1	0.5	22.1	(5.9)					4.6		0.1		(0.4)		21.7		2.3		0.3		2.7
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ 18.2		$ 18.2		$ (3.9)	$ (34.1)			$ (34.1)	$ (38.7)	$ 0.5	$ 0.4	$ 0.6	$ 1.0	$ 19.2	$ (2.5)	$ 4.9	$ 2.6	$ (1.5)	$ (1.8)	$ (39.6)	$ (42.3)