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
	Mar. 31, 2014	Mar. 31, 2013
Change in unrealized gain / (loss)	$ (5.9)
Gain (Loss) on Derivative Instruments, Net, Pretax	(7.8)
Derivative, Gain (Loss) on Derivative, Net	(1.9)
NYMEX Coal Contract [Member]
Change in unrealized gain / (loss)	(0.1)
Gain (Loss) on Derivative Instruments, Net, Pretax		0.5
Derivative, Gain (Loss) on Derivative, Net	0.1	0.5
Commodity Contract - FTR [Member]
Change in unrealized gain / (loss)		(16.5)
Gain (Loss) on Derivative Instruments, Net, Pretax		0.9
Derivative, Gain (Loss) on Derivative, Net		(15.6)
Commodity Contract - Heating Oil [Member]
Change in unrealized gain / (loss)	(0.3)	(16.5)
Gain (Loss) on Derivative Instruments, Net, Pretax	(0.3)	0.4
Derivative, Gain (Loss) on Derivative, Net		(16.1)
Forward Contract Power [Member]
Change in unrealized gain / (loss)	(5.5)
Gain (Loss) on Derivative Instruments, Net, Pretax	(7.5)
Derivative, Gain (Loss) on Derivative, Net	(2.0)
DP&L [Member]
Change in unrealized gain / (loss)	(5.9)
Gain (Loss) on Derivative Instruments, Net, Pretax	(7.2)
Derivative, Gain (Loss) on Derivative, Net	(1.3)
DP&L [Member] | NYMEX Coal Contract [Member]
Change in unrealized gain / (loss)	(0.1)
Gain (Loss) on Derivative Instruments, Net, Pretax		0.5
Derivative, Gain (Loss) on Derivative, Net	0.1	0.5
DP&L [Member] | Commodity Contract - FTR [Member]
Change in unrealized gain / (loss)		(10.4)
Gain (Loss) on Derivative Instruments, Net, Pretax		1.2
Derivative, Gain (Loss) on Derivative, Net		(9.2)
DP&L [Member] | Commodity Contract - Heating Oil [Member]
Change in unrealized gain / (loss)	(0.3)	(10.4)
Gain (Loss) on Derivative Instruments, Net, Pretax	(0.3)	0.7
Derivative, Gain (Loss) on Derivative, Net		(9.7)
DP&L [Member] | Forward Contract Power [Member]
Change in unrealized gain / (loss)	(5.5)
Gain (Loss) on Derivative Instruments, Net, Pretax	(6.9)
Derivative, Gain (Loss) on Derivative, Net	(1.4)
Revenue [Member] | DP&L [Member]
Derivative, Gain (Loss) on Derivative, Net	0.8
Revenue [Member] | DP&L [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net		(1.1)
Revenue [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net		(1.1)
Revenue [Member] | DP&L [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	0.8
Purchased Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(7.8)
Purchased Power [Member] | NYMEX Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net		0.5
Purchased Power [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net		(15.6)
Purchased Power [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.3)	(16.1)
Purchased Power [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(7.5)
Purchased Power [Member] | DP&L [Member]
Derivative, Gain (Loss) on Derivative, Net	(8.0)
Purchased Power [Member] | DP&L [Member] | NYMEX Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net		0.5
Purchased Power [Member] | DP&L [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net		(8.1)
Purchased Power [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.3)	(8.6)
Purchased Power [Member] | DP&L [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	$ (7.7)