Derivative Instruments and Hedging Activities (Fair Value and Balance Sheet Location (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivative Liability, Fair Value	$ 10.3
DP&L [Member]
Derivative Liability, Fair Value	10.1
Total Assets [Member]
Derivative Asset, Fair Value	21.6	7.5
Derivative, Fair Value, Net	16.7	4.2
Derivative, Collateral, net		(0.2)
Derivative, Fair Value, Offset, Net	(4.9)	(3.1)
Total Assets [Member] | DP&L [Member]
Derivative Asset, Fair Value	21.7	7.6
Derivative, Fair Value, Net	16.8	4.3
Derivative, Collateral, net		(0.2)
Derivative, Fair Value, Offset, Net	(4.9)	(3.1)
Total Liabilities [Member]
Derivative, Fair Value, Net	1.0	34.5
Derivative, Collateral, net	(4.4)	(5.1)
Derivative, Fair Value, Offset, Net	(4.9)	(3.1)
Derivative Liability, Fair Value	10.3	42.7
Total Liabilities [Member] | DP&L [Member]
Derivative, Fair Value, Net	1.0	5.1
Derivative, Collateral, net	(4.2)	(3.5)
Derivative, Fair Value, Offset, Net	(4.9)	(3.1)
Derivative Liability, Fair Value	10.1	11.7
Commodity Contract - Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value	0.1
Derivative, Fair Value, Net	0.1
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	5.1	2.7
Derivative, Fair Value, Net	2.5	1.2
Derivative, Fair Value, Offset, Net	(2.6)	(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	5.2	2.8
Derivative, Fair Value, Net	2.6	1.3
Derivative, Fair Value, Offset, Net	(2.6)	(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	0.3	0.6
Derivative, Collateral, net	(2.1)	(2.0)
Derivative, Fair Value, Offset, Net	(2.6)	(1.5)
Derivative Liability, Fair Value	5.0	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	0.3	0.7
Derivative, Collateral, net	(1.8)	(0.5)
Derivative, Fair Value, Offset, Net	(2.6)	(1.5)
Derivative Liability, Fair Value	4.7	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	0.4	0.1
Derivative, Collateral, net		(0.1)
Derivative, Fair Value, Offset, Net	(0.7)	(0.6)
Derivative Liability, Fair Value	1.1	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, Collateral, net	(0.1)
Derivative, Fair Value, Offset, Net	(0.7)	(0.6)
Derivative Liability, Fair Value	1.1	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	12.7	3.6
Derivative, Fair Value, Net	12.0	3.0
Derivative, Fair Value, Offset, Net	(0.7)	(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	12.7	3.6
Derivative, Fair Value, Net	12.0	3.0
Derivative, Fair Value, Offset, Net	(0.7)	(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	0.4
Derivative, Fair Value, Net	0.4
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	0.4	0.2
Derivative, Fair Value, Net	0.4
Derivative, Collateral, net		(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	0.1	0.2
Derivative, Fair Value, Net	0.1
Derivative, Collateral, net		(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	1.4	0.5
Derivative, Fair Value, Net	0.3
Derivative, Fair Value, Offset, Net	(1.1)	(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	1.4	0.5
Derivative, Fair Value, Net	0.3
Derivative, Fair Value, Offset, Net	(1.1)	(0.5)
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Fair Value, Net	0.3	4.1
Derivative, Collateral, net	(2.3)	(2.1)
Derivative, Fair Value, Offset, Net	(1.1)	(0.5)
Derivative Liability, Fair Value	3.7	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	0.4	4.1
Derivative, Collateral, net	(2.3)	(2.1)
Derivative, Fair Value, Offset, Net	(1.1)	(0.5)
Derivative Liability, Fair Value	3.8	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		(0.9)
Derivative, Fair Value, Offset, Net	(0.5)	(0.5)
Derivative Liability, Fair Value	0.5	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		(0.9)
Derivative, Fair Value, Offset, Net	(0.5)	(0.5)
Derivative Liability, Fair Value	0.5	1.5
Cash Flow Hedging [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member]
Derivative Asset, Fair Value	1.9	0.5
Derivative, Fair Value, Net	1.4
Derivative, Fair Value, Offset, Net	(0.5)	(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	1.9	0.5
Derivative, Fair Value, Net	1.4
Derivative, Fair Value, Offset, Net	(0.5)	(0.5)
Cash Flow Hedging [Member] | Interest Rate Contract [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative, Fair Value, Net		29.5
Derivative Liability, Fair Value		$ 29.5