Derivative Instruments and Hedging Activities (Fair Value and Balance Sheet Location (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
DP&L [Member]
Derivative Liability, Fair Value	$ 22.9
Total Assets [Member]
Derivative Asset, Fair Value	6.0	7.5
Derivative, Fair Value, Net	1.3	4.2
Derivative, Collateral, net	(0.2)	(0.2)
Derivative, Fair Value, Offset, Net	(4.5)	(3.1)
Total Assets [Member] | DP&L [Member]
Derivative Asset, Fair Value	6.8	7.6
Derivative, Fair Value, Net	2.1	4.3
Derivative, Collateral, net	(0.2)	(0.2)
Derivative, Fair Value, Offset, Net	(4.5)	(3.1)
Total Liabilities [Member]
Derivative, Fair Value, Net	27.7	34.5
Derivative, Collateral, net	(14.3)	(5.1)
Derivative, Fair Value, Offset, Net	(4.5)	(3.1)
Derivative Liability, Fair Value	46.5	42.7
Total Liabilities [Member] | DP&L [Member]
Derivative, Fair Value, Net	4.5	5.1
Derivative, Collateral, net	(13.9)	(3.5)
Derivative, Fair Value, Offset, Net	(4.5)	(3.1)
Derivative Liability, Fair Value	22.9	11.7
Not Designated as Hedging Instrument [Member]
Derivative Liability, Fair Value	23.3
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	4.5	2.7
Derivative, Fair Value, Net	0.7	1.2
Derivative, Fair Value, Offset, Net	(3.8)	(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	5.3	2.8
Derivative, Fair Value, Net	1.5	1.3
Derivative, Fair Value, Offset, Net	(3.8)	(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	0.6	0.6
Derivative, Collateral, net	(5.5)	(2.0)
Derivative, Fair Value, Offset, Net	(3.8)	(1.5)
Derivative Liability, Fair Value	9.9	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	0.6	0.7
Derivative, Collateral, net	(5.1)	(0.5)
Derivative, Fair Value, Offset, Net	(3.8)	(1.5)
Derivative Liability, Fair Value	9.5	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	0.5	0.1
Derivative, Collateral, net	(1.5)	(0.1)
Derivative, Fair Value, Offset, Net	(0.6)	(0.6)
Derivative Liability, Fair Value	2.6	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	0.5	0.1
Derivative, Collateral, net	(1.5)
Derivative, Fair Value, Offset, Net	(0.6)	(0.6)
Derivative Liability, Fair Value	2.6	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	1.1	3.6
Derivative, Fair Value, Net	0.5	3.0
Derivative, Fair Value, Offset, Net	(0.6)	(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	1.1	3.6
Derivative, Fair Value, Net	0.5	3.0
Derivative, Fair Value, Offset, Net	(0.6)	(0.6)
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Fair Value, Net		0.1
Derivative Liability, Fair Value		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		0.1
Derivative Liability, Fair Value		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	0.2	0.2
Derivative, Collateral, net	(0.2)	(0.2)
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	0.2
Derivative, Collateral, net	(0.2)	(0.2)
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value	0.2	0.5
Derivative, Fair Value, Net	0.1
Derivative, Fair Value, Offset, Net	(0.1)	(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	0.2	0.5
Derivative, Fair Value, Net	0.1
Derivative, Fair Value, Offset, Net	(0.1)	(0.5)
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Fair Value, Net	2.6	4.1
Derivative, Collateral, net	(6.2)	(2.1)
Derivative, Fair Value, Offset, Net	(0.1)	(0.5)
Derivative Liability, Fair Value	8.9	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	2.6	4.1
Derivative, Collateral, net	(6.2)	(2.1)
Derivative, Fair Value, Offset, Net	(0.1)	(0.5)
Derivative Liability, Fair Value	8.9	6.7
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member]
Derivative, Fair Value, Net	0.8	0.1
Derivative, Collateral, net	(1.1)	(0.9)
Derivative, Fair Value, Offset, Net		(0.5)
Derivative Liability, Fair Value	1.9	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	0.8	0.1
Derivative, Collateral, net	(1.1)	(0.9)
Derivative, Fair Value, Offset, Net		(0.5)
Derivative Liability, Fair Value	1.9	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
Derivative, Fair Value, Offset, Net		(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
Derivative, Fair Value, Offset, Net		(0.5)
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Fair Value, Net	23.2	29.5
Derivative Liability, Fair Value	$ 23.2	$ 29.5