Derivative Instruments and Hedging Activities (Fair Value and Balance Sheet Location (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
Total Assets [Member]
Derivative Asset, Fair Value	20,600,000	14,900,000
Derivative, Fair Value, Net	11,600,000	8,300,000
Derivative, Fair Value, Offset, Net	(9,000,000)	(6,600,000)
Total Assets [Member] | DP&L [Member]
Derivative Asset, Fair Value	20,800,000	15,100,000
Derivative, Fair Value, Net	11,800,000	8,500,000
Derivative, Fair Value, Offset, Net	(9,000,000)	(6,600,000)
Total Liabilities [Member]
Derivative, Fair Value, Net	1,000,000	700,000
Derivative, Collateral, net	(10,700,000)	(4,900,000)
Derivative, Fair Value, Offset, Net	(9,000,000)	(6,600,000)
Derivative Liability, Fair Value	20,700,000	12,200,000
Total Liabilities [Member] | DP&L [Member]
Derivative, Fair Value, Net	1,200,000	800,000
Derivative, Collateral, net	(10,700,000)	(4,900,000)
Derivative, Fair Value, Offset, Net	(9,000,000)	(6,600,000)
Derivative Liability, Fair Value	20,900,000	12,300,000
Commodity Contract - Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value	300,000
Derivative, Fair Value, Net	300,000
Commodity Contract - Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Collateral, net	(300,000)
Derivative Liability, Fair Value	300,000
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, Fair Value, Net	1,000,000
Derivative, Collateral, net	(8,800,000)
Derivative, Fair Value, Offset, Net	(3,200,000)
Derivative Liability, Fair Value	13,000,000
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | DP&L [Member]
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)
Derivative Liability, Fair Value	13,100,000	7,500,000
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Deferred Credit [Member]
Derivative, Collateral, net		(4,100,000)
Derivative, Fair Value, Offset, Net		(3,400,000)
Derivative Liability, Fair Value		7,500,000
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member]
Derivative, Fair Value, Offset, Net	(600,000)	(900,000)
Derivative Liability, Fair Value	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, Fair Value, Net	100,000	100,000
Derivative, Fair Value, Offset, Net	(600,000)	(900,000)
Derivative Liability, Fair Value	700,000	1,000,000
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)
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Fair Value, Net		600,000
Derivative Liability, Fair Value		600,000
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | DP&L [Member]
Derivative, Fair Value, Net		600,000
Derivative Liability, Fair Value		600,000
Not Designated as Hedging Instrument [Member] | Commodity Contract - Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | DP&L [Member]
Derivative Asset, Fair Value	300,000
Derivative, Fair Value, Net	300,000
Not Designated as Hedging Instrument [Member] | Commodity Contract - Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Collateral, net		(400,000)
Derivative Liability, Fair Value		400,000
Not Designated as Hedging Instrument [Member] | Commodity Contract - Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | DP&L [Member]
Derivative, Collateral, net	(300,000)	(400,000)
Derivative Liability, Fair Value	300,000	400,000
Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Collateral, net		(100,000)
Derivative Liability, Fair Value		100,000
Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | DP&L [Member]
Derivative, Collateral, net		(100,000)
Derivative Liability, Fair Value		100,000
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value	5,200,000	5,600,000
Derivative, Fair Value, Net	2,700,000	3,600,000
Derivative, Fair Value, Offset, Net	(2,500,000)	(2,000,000)
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | DP&L [Member]
Derivative Asset, Fair Value	5,200,000	5,600,000
Derivative, Fair Value, Net	2,700,000	3,600,000
Derivative, Fair Value, Offset, Net	(2,500,000)	(2,000,000)
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Fair Value, Net		100,000
Derivative, Collateral, net	(1,600,000)
Derivative, Fair Value, Offset, Net	(2,500,000)	(2,000,000)
Derivative Liability, Fair Value	4,100,000	2,100,000
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | DP&L [Member]
Derivative, Fair Value, Net		100,000
Derivative, Collateral, net	(1,600,000)
Derivative, Fair Value, Offset, Net	(2,500,000)	(2,000,000)
Derivative Liability, Fair Value	4,100,000	2,100,000
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member]
Derivative, Collateral, net		(300,000)
Derivative, Fair Value, Offset, Net	(2,700,000)	(300,000)
Derivative Liability, Fair Value	2,700,000	600,000
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | DP&L [Member]
Derivative, Collateral, net		(300,000)
Derivative, Fair Value, Offset, Net	(2,700,000)	(300,000)
Derivative Liability, Fair Value	2,700,000	600,000
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member]
Derivative Asset, Fair Value	3,800,000	300,000
Derivative, Fair Value, Net	1,100,000
Derivative, Fair Value, Offset, Net	(2,700,000)	(300,000)
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | DP&L [Member]
Derivative Asset, Fair Value	3,800,000	300,000
Derivative, Fair Value, Net	1,100,000
Derivative, Fair Value, Offset, Net	$ (2,700,000)	$ (300,000)