Derivative Instruments and Hedging Activities (Fair Value and Balance Sheet Location (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivative Liability, Fair Value	$ 14.4
DP&L [Member]
Derivative Liability, Fair Value	14.1
Total Assets [Member]
Derivative Asset, Fair Value	22.3	7.5
Derivative, Fair Value, Net	15.3	4.2
Derivative, Collateral, net		(0.2)
Derivative, Fair Value, Offset, Net	(7.0)	(3.1)
Total Assets [Member] | DP&L [Member]
Derivative Asset, Fair Value	22.5	7.6
Derivative, Fair Value, Net	15.5	4.3
Derivative, Collateral, net		(0.2)
Derivative, Fair Value, Offset, Net	(7.0)	(3.1)
Total Liabilities [Member]
Derivative, Fair Value, Net	12.2	34.5
Derivative, Collateral, net	(4.7)	(5.1)
Derivative, Fair Value, Offset, Net	(7.0)	(3.1)
Derivative Liability, Fair Value	23.9	42.7
Total Liabilities [Member] | DP&L [Member]
Derivative, Fair Value, Net	2.8	5.1
Derivative, Collateral, net	(4.3)	(3.5)
Derivative, Fair Value, Offset, Net	(7.0)	(3.1)
Derivative Liability, Fair Value	14.1	11.7
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	7.8	2.7
Derivative, Fair Value, Net	2.6	1.2
Derivative, Fair Value, Offset, Net	(5.2)	(1.5)
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	8.0	2.8
Derivative, Fair Value, Net	2.8	1.3
Derivative, Fair Value, Offset, Net	(5.2)	(1.5)
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Fair Value, Net	1.0	0.6
Derivative, Collateral, net	(0.6)	(2.0)
Derivative, Fair Value, Offset, Net	(5.2)	(1.5)
Derivative Liability, Fair Value	6.8	4.1
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	1.1	0.7
Derivative, Collateral, net	(0.2)	(0.5)
Derivative, Fair Value, Offset, Net	(5.2)	(1.5)
Derivative Liability, Fair Value	6.5	2.7
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member]
Derivative, Fair Value, Net	0.3	0.1
Derivative, Collateral, net		(0.1)
Derivative, Fair Value, Offset, Net	(0.5)	(0.6)
Derivative Liability, Fair Value	0.8	0.8
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	0.3	0.1
Derivative, Fair Value, Offset, Net	(0.5)	(0.6)
Derivative Liability, Fair Value	0.8	0.7
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member]
Derivative Asset, Fair Value	11.6	3.6
Derivative, Fair Value, Net	11.1	3.0
Derivative, Fair Value, Offset, Net	(0.5)	(0.6)
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	11.6	3.6
Derivative, Fair Value, Net	11.1	3.0
Derivative, Fair Value, Offset, Net	(0.5)	(0.6)
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | DP&L [Member]
Derivative Asset, Fair Value	0.1
Derivative, Fair Value, Offset, Net	(0.1)
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Fair Value, Net	0.9	0.1
Derivative, Fair Value, Offset, Net	(0.1)
Derivative Liability, Fair Value	1.0	0.1
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	0.9	0.1
Derivative, Fair Value, Offset, Net	(0.1)
Derivative Liability, Fair Value	1.0	0.1
Not Designated as Hedging Instrument [Member] | Commodity Contract - Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value	0.1	0.2
Derivative, Collateral, net		(0.2)
Derivative, Fair Value, Offset, Net	(0.1)
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		0.2
Derivative, Collateral, net		(0.2)
Not Designated as Hedging Instrument [Member] | Commodity Contract - Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Collateral, net	(0.1)
Derivative Liability, Fair Value	0.1
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	(0.1)
Derivative Liability, Fair Value	0.1
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value	2.3	0.5
Derivative, Fair Value, Net	1.3
Derivative, Fair Value, Offset, Net	(1.0)	(0.5)
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	2.3	0.5
Derivative, Fair Value, Net	1.3
Derivative, Fair Value, Offset, Net	(1.0)	(0.5)
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Fair Value, Net	0.5	4.1
Derivative, Collateral, net	(3.4)	(2.1)
Derivative, Fair Value, Offset, Net	(1.0)	(0.5)
Derivative Liability, Fair Value	4.9	6.7
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | DP&L [Member]
Derivative, Fair Value, Net	0.5	4.1
Derivative, Collateral, net	(3.4)	(2.1)
Derivative, Fair Value, Offset, Net	(1.0)	(0.5)
Derivative Liability, Fair Value	4.9	6.7
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member]
Derivative, Fair Value, Net		0.1
Derivative, Collateral, net	(0.6)	(0.9)
Derivative, Fair Value, Offset, Net	(0.2)	(0.5)
Derivative Liability, Fair Value	0.8	1.5
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | DP&L [Member]
Derivative, Fair Value, Net		0.1
Derivative, Collateral, net	(0.6)	(0.9)
Derivative, Fair Value, Offset, Net	(0.2)	(0.5)
Derivative Liability, Fair Value	0.8	1.5
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member]
Derivative Asset, Fair Value	0.5	0.5
Derivative, Fair Value, Net	0.3
Derivative, Fair Value, Offset, Net	(0.2)	(0.5)
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | DP&L [Member]
Derivative Asset, Fair Value	0.5	0.5
Derivative, Fair Value, Net	0.3
Derivative, Fair Value, Offset, Net	(0.2)	(0.5)
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Fair Value, Net	9.5	29.5
Derivative Liability, Fair Value	$ 9.5	$ 29.5