Fair Value Measurements (Fair Value of Assets and Liabilities Measured on a Nonrecurring Basis) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Carrying Value		$ 2,534.2	$ 2,563.8
Goodwill		452.8	759.1	2,576.3
Goodwill Impairment	1,850.0	306.3	1,817.2
Goodwill Allocated to DP&L Reporting Unit		2,400.0
Estimate of Fair Value, Fair Value Disclosure [Member]
Goodwill Allocated to DP&L Reporting Unit		306.3
Level 3 [Member]
Goodwill Impairment		317.0
DP&L [Member]
Fixed asset impairment	80.8
Goodwill		317.0	623.3	2,440.5
Goodwill Impairment		(306.3)	(1,817.2)
DP&L [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Goodwill Allocated to DP&L Reporting Unit			1,817.2
DP&L [Member] | Level 1 [Member]
Goodwill			2,440.5
DP&L [Member] | Level 3 [Member]
Goodwill Impairment			623.3
Conesville Unit 4 [Member]
Carrying Value		26.2
Fixed asset impairment		26.2
Fair Value		0
Conesville Unit 4 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value		26.2
Conesville Unit 4 [Member] | DP&L [Member]
Carrying Value		30.0	97.5
Fixed asset impairment		10.0	72.5
Fair Value		0	25.0
Goodwill Impairment			72.5
Conesville Unit 4 [Member] | DP&L [Member] | Level 3 [Member]
Fair Value		20.0	25.0
East Bend Station [Member] | DP&L [Member]
Carrying Value		76.0
Fixed asset impairment		76.0
Hutchings Station [Member] | DP&L [Member]
Carrying Value			8.3
Goodwill Impairment			$ 8.3