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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Change in unrealized gain / (loss)	$ (2.2)	$ 1.5	$ (7.5)	$ 10.7
Gain (Loss) on Derivative Instruments, Net, Pretax	(2.0)	(0.7)	(2.8)	1.7
Regulatory (asset)/liability				(0.1)
Derivative, Gain (Loss) on Derivative, Net	(4.2)	0.8	(10.3)	12.4
Commodity Contract - FTR [Member]
Change in unrealized gain / (loss)	0.3	1.3	(1.2)	0.4
Gain (Loss) on Derivative Instruments, Net, Pretax	0.1		0.7	1.2
Derivative, Gain (Loss) on Derivative, Net	0.4	1.3	(0.5)	1.6
Commodity Contract - Heating Oil [Member]
Change in unrealized gain / (loss)	(0.2)	0.1	(0.3)	(0.2)
Gain (Loss) on Derivative Instruments, Net, Pretax		0.1	0.1
Regulatory (asset)/liability				(0.1)
Derivative, Gain (Loss) on Derivative, Net	(0.2)	0.2	(0.2)	(0.2)
Forward Contract Power [Member]
Change in unrealized gain / (loss)	(2.3)	0.1	(6.0)	10.5
Gain (Loss) on Derivative Instruments, Net, Pretax	(2.1)	(0.8)	(3.6)	0.5
Derivative, Gain (Loss) on Derivative, Net	(4.4)	(0.7)	(9.6)	11.0
DP&L [Member]
Change in unrealized gain / (loss)	(2.6)	1.3	(7.2)	9.1
Gain (Loss) on Derivative Instruments, Net, Pretax	(2.0)	(0.7)	(9.4)	2.3
Regulatory (asset)/liability				(0.1)
Derivative, Gain (Loss) on Derivative, Net	(4.6)	0.6	(2.2)	11.4
DP&L [Member] | NYMEX Coal Contract [Member]
Change in unrealized gain / (loss)			(0.3)	(0.2)
Gain (Loss) on Derivative Instruments, Net, Pretax			(0.2)
Regulatory (asset)/liability				(0.1)
Derivative, Gain (Loss) on Derivative, Net			0.1	(0.2)
DP&L [Member] | Commodity Contract - FTR [Member]
Change in unrealized gain / (loss)	0.3	1.3		8.9
Gain (Loss) on Derivative Instruments, Net, Pretax	0.1			1.1
Derivative, Gain (Loss) on Derivative, Net	0.4	1.3		10.0
DP&L [Member] | Commodity Contract - Heating Oil [Member]
Change in unrealized gain / (loss)	(0.2)	0.1	(1.2)	0.4
Gain (Loss) on Derivative Instruments, Net, Pretax		0.1	(0.5)	1.2
Derivative, Gain (Loss) on Derivative, Net	(0.2)	0.2	0.7	1.6
DP&L [Member] | Forward Contract Power [Member]
Change in unrealized gain / (loss)	(2.7)	(0.1)	(5.7)
Gain (Loss) on Derivative Instruments, Net, Pretax	(2.1)	(0.8)	(8.7)
Derivative, Gain (Loss) on Derivative, Net	(4.8)	(0.9)	(3.0)
Revenue [Member] | DP&L [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.3)	0.1	1.0	0.2
Revenue [Member] | DP&L [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net				0.2
Revenue [Member] | DP&L [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.3)	0.1	1.0
Fuel [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.1)	0.1	(0.1)	(0.1)
Fuel [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.1)	0.1	(0.1)	(0.1)
Fuel [Member] | DP&L [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.1)	0.1	(0.1)	(0.1)
Fuel [Member] | DP&L [Member] | NYMEX Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net			(0.1)	(0.1)
Fuel [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.1)	0.1
O&M [Member]
Derivative, Gain (Loss) on Derivative, Net		0.1
O&M [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net		0.1
O&M [Member] | DP&L [Member]
Derivative, Gain (Loss) on Derivative, Net		0.1
O&M [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net		0.1
Purchased Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(4.0)	0.6	(10.1)	12.6
Purchased Power [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	0.4	1.3	(0.5)	1.6
Purchased Power [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(4.4)	(0.7)	(9.6)	11.0
Purchased Power [Member] | DP&L [Member]
Derivative, Gain (Loss) on Derivative, Net	(4.1)	0.3	(10.2)	11.4
Purchased Power [Member] | DP&L [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	0.4	1.3		9.8
Purchased Power [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net			(0.5)	1.6
Purchased Power [Member] | DP&L [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(4.5)	(1.0)	(9.7)
Regulatory Asset Liability [Member]
Regulatory (asset)/liability	(0.1)		(0.1)
Regulatory Asset Liability [Member] | Commodity Contract - Heating Oil [Member]
Regulatory (asset)/liability	(0.1)		(0.1)
Regulatory Asset Liability [Member] | DP&L [Member]
Regulatory (asset)/liability			(0.1)
Regulatory Asset Liability [Member] | DP&L [Member] | NYMEX Coal Contract [Member]
Regulatory (asset)/liability			(0.1)
Not Designated as Hedging Instrument [Member] | Regulatory Asset Liability [Member] | DP&L [Member]
Regulatory (asset)/liability	(0.1)
Not Designated as Hedging Instrument [Member] | Regulatory Asset Liability [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Regulatory (asset)/liability	$ (0.1)