Derivative Instruments and Hedging Activities (Classification within the Condensed Consolidated Statements of Results of Operations or Balance Sheets of the Gains and Losses) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Change in unrealized gain / (loss)	$ 0.7	$ 17.2	$ (5.3)	$ 9.2
Gain (Loss) on Derivative Instruments, Net, Pretax	1.1	1.5	(0.8)	2.5
Regulatory (asset)/liability		(0.1)		(0.1)
Derivative, Gain (Loss) on Derivative, Net	1.8	18.7	(6.1)	11.7
Commodity Contract - FTR [Member]
Change in unrealized gain / (loss)	(1.2)	(0.9)	(1.5)	(0.9)
Gain (Loss) on Derivative Instruments, Net, Pretax	0.6	0.6	0.6	1.2
Derivative, Gain (Loss) on Derivative, Net	(0.6)	(0.3)	(0.9)	0.3
Commodity Contract - Heating Oil [Member]
Change in unrealized gain / (loss)	0.1	(0.3)	(0.1)	(0.3)
Gain (Loss) on Derivative Instruments, Net, Pretax			0.1
Regulatory (asset)/liability		(0.1)		(0.1)
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.3)		(0.3)
Forward Contract Power [Member]
Change in unrealized gain / (loss)	1.8	18.4	(3.7)	10.4
Gain (Loss) on Derivative Instruments, Net, Pretax	0.5	0.9	(1.5)	1.3
Derivative, Gain (Loss) on Derivative, Net	2.3	19.3	(5.2)	11.7
DP&L [Member]
Change in unrealized gain / (loss)	1.3	16.6	(4.7)	7.9
Gain (Loss) on Derivative Instruments, Net, Pretax	1.2	1.8	(4.8)	3.1
Regulatory (asset)/liability		(0.1)		(0.1)
Derivative, Gain (Loss) on Derivative, Net	2.5	18.4	(0.1)	11.0
DP&L [Member] | NYMEX Coal Contract [Member]
Change in unrealized gain / (loss)			(0.1)	(0.3)
Regulatory (asset)/liability				(0.1)
Derivative, Gain (Loss) on Derivative, Net			0.1	(0.3)
DP&L [Member] | Commodity Contract - FTR [Member]
Change in unrealized gain / (loss)	(1.2)	(0.9)		9.1
Gain (Loss) on Derivative Instruments, Net, Pretax	0.6	0.6		1.9
Derivative, Gain (Loss) on Derivative, Net	(0.6)	(0.3)		11.0
DP&L [Member] | Commodity Contract - Heating Oil [Member]
Change in unrealized gain / (loss)	0.1	(0.3)	(1.5)	(0.9)
Gain (Loss) on Derivative Instruments, Net, Pretax			(0.9)	1.2
Regulatory (asset)/liability		(0.1)
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.3)	0.6	0.3
DP&L [Member] | Forward Contract Power [Member]
Change in unrealized gain / (loss)	2.4	17.8	(3.1)
Gain (Loss) on Derivative Instruments, Net, Pretax	0.6	1.2	(3.9)
Derivative, Gain (Loss) on Derivative, Net	3.0	19.0	(0.8)
Revenue [Member] | DP&L [Member]
Derivative, Gain (Loss) on Derivative, Net	0.7	(0.1)	1.4	0.3
Revenue [Member] | DP&L [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net				0.3
Revenue [Member] | DP&L [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	0.7	(0.1)	1.4
Fuel [Member]
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.2)		(0.2)
Fuel [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.2)		(0.2)
Fuel [Member] | DP&L [Member]
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.2)		(0.2)
Fuel [Member] | DP&L [Member] | NYMEX Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net				(0.2)
Fuel [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.2)
Purchased Power [Member]
Derivative, Gain (Loss) on Derivative, Net	1.7	19.0	(6.1)	12.0
Purchased Power [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.6)	(0.3)	(0.9)	0.3
Purchased Power [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	2.3	19.3	(5.2)	11.7
Purchased Power [Member] | DP&L [Member]
Derivative, Gain (Loss) on Derivative, Net	1.7	18.8	(6.2)	11.0
Purchased Power [Member] | DP&L [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.6)	(0.3)		10.7
Purchased Power [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net			(0.9)	0.3
Purchased Power [Member] | DP&L [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	$ 2.3	$ 19.1	$ (5.3)