Derivative Instruments and Hedging Activities (Fair Values of Derivative Instruments Designated as Hedging Instruments) (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Derivative Liability, Fair Value	$ (20,700,000)
DP&L [Member]
Derivative Liability, Fair Value	(20,900,000)
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value	4,900,000	5,500,000
Derivative, Fair Value, Net	1,700,000	2,100,000
Derivative, Fair Value, Offset, Net	(3,200,000)	(3,400,000)
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | DP&L [Member]
Derivative Asset, Fair Value	5,000,000	5,600,000
Derivative, Fair Value, Net	1,800,000	2,200,000
Derivative, Fair Value, Offset, Net	(3,200,000)	(3,400,000)
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative Liability, Fair Value	(13,000,000)
Derivative, Fair Value, Net	1,000,000
Derivative, Collateral, net	(8,800,000)
Derivative, Fair Value, Offset, Net	(3,200,000)
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | DP&L [Member]
Derivative Liability, Fair Value	(13,100,000)	(7,500,000)
Derivative, Fair Value, Net	1,100,000
Derivative, Collateral, net	(8,800,000)	(4,100,000)
Derivative, Fair Value, Offset, Net	(3,200,000)	(3,400,000)
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Deferred Credit [Member]
Derivative Liability, Fair Value		(7,500,000)
Derivative, Collateral, net		(4,100,000)
Derivative, Fair Value, Offset, Net		(3,400,000)
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member]
Derivative Liability, Fair Value	(600,000)	(900,000)
Derivative, Fair Value, Offset, Net	(600,000)	(900,000)
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | DP&L [Member]
Derivative Liability, Fair Value	(700,000)	(1,000,000)
Derivative, Fair Value, Net	100,000	100,000
Derivative, Fair Value, Offset, Net	(600,000)	(900,000)
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member]
Derivative Asset, Fair Value	6,400,000	3,500,000
Derivative, Fair Value, Net	5,800,000	2,600,000
Derivative, Fair Value, Offset, Net	(600,000)	(900,000)
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | DP&L [Member]
Derivative Asset, Fair Value	6,500,000	3,600,000
Derivative, Fair Value, Net	5,900,000	2,700,000
Derivative, Fair Value, Offset, Net	$ (600,000)	$ (900,000)