Fair Value Measurements (Fair Value and Redemption Frequency) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Total Fair Value	$ 11.0	$ 10.1
DP&L [Member]
Total Fair Value	11.0	10.1
Equity Securities [Member]
Total Fair Value	5.2	4.4
Equity Securities [Member] | DP&L [Member]
Total Fair Value	5.2	4.4
Debt Securities [Member]
Total Fair Value	5.5	5.5
Debt Securities [Member] | DP&L [Member]
Total Fair Value	5.5	5.5
Multi Strategy Fund [Member]
Total Fair Value	0.3	0.2
Multi Strategy Fund [Member] | DP&L [Member]
Total Fair Value	$ 0.3	$ 0.2