Derivative Instruments and Hedging Activities (Fair Values of Derivative Instruments Not Designated as Hedging Instruments) (Details) (USD $) In Millions	Jun. 30, 2011		Dec. 31, 2010
Derivative Liability, Fair Value	$ (9.9)
DP&L [Member] | MTM position [Member]
Derivative Assets (Liabilities), at Fair Value, Net	27.1	[1]
Derivative Asset, Fair Value, Not Offset Amount	10.7
Derivative, Fair Value Counterparty and Collateral, Netting	16.4	[2]
DP&L [Member] | MTM position [Member] | Short-term Derivative Positions [Member]
Derivative Assets (Liabilities), at Fair Value, Net	15.3	[1]
Derivative Asset, Fair Value, Not Offset Amount	5.9
Derivative, Fair Value Counterparty and Collateral, Netting	(9.4)	[2]
DP&L [Member] | MTM position [Member] | Long-term Derivative Positions [Member]
Derivative Liability, Fair Value	(11.8)	[1]
Derivative Asset, Fair Value, Not Offset Amount	4.8
Derivative, Fair Value Counterparty and Collateral, Netting	(7.0)	[2]
MTM position [Member]
Derivative Assets (Liabilities), at Fair Value, Net	32.7	[1]
Derivative Asset, Fair Value, Not Offset Amount	18.3
Derivative, Fair Value Counterparty and Collateral, Netting	14.4	[2]
MTM position [Member] | Short-term Derivative Positions [Member]
Derivative Assets (Liabilities), at Fair Value, Net	17.0	[1]
Derivative Asset, Fair Value, Not Offset Amount	8.6
Derivative, Fair Value Counterparty and Collateral, Netting	8.4	[2]
MTM position [Member] | Long-term Derivative Positions [Member]
Derivative Liability, Fair Value	15.7	[1]
Derivative Asset, Fair Value, Not Offset Amount	9.7
Derivative, Fair Value Counterparty and Collateral, Netting	6.0	[2]
MTM position [Member] | Long-term Derivative Positions [Member] | Derivative Instruments Not Designated as Hedging Instruments [Member]
Derivative, Fair Value, Not Offset, Net			24.6	[1]
Derivative, Fair Value Counterparty and Collateral, Netting			15.6	[2]
Derivative, Fair Value, Offset, Net			9.0
MTM position [Member] | Derivative Instruments Not Designated as Hedging Instruments [Member]
Derivative, Fair Value, Not Offset, Net			39.3	[1]
Derivative, Fair Value Counterparty and Collateral, Netting			23.5	[2]
Derivative, Fair Value, Offset, Net			15.8
Futures [Member] | Short-term Derivative Positions [Member] | Derivative Instruments Not Designated as Hedging Instruments [Member]
Derivative Asset, Fair Value			0.5	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting			(0.5)	[2]
Futures [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative Liability, Fair Value, Not Offset Amount
DP&L [Member] | Heating Oil [Member] | Short-term Derivative Positions [Member]
Derivative Asset, Fair Value	2.6	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	2.6	[2]
DP&L [Member] | Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount
DP&L [Member] | Heating Oil [Member] | Long-term Derivative Positions [Member]
Derivative Asset, Fair Value	0.7	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	0.7	[2]
DP&L [Member] | Heating Oil [Member] | Long-term Derivative Positions [Member] | Other Deferred Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount
Heating Oil [Member] | Short-term Derivative Positions [Member]
Derivative Asset, Fair Value	2.6	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	(2.6)	[2]
Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount
Heating Oil [Member] | Long-term Derivative Positions [Member]
Derivative Asset, Fair Value	0.7	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	0.7	[2]
Heating Oil [Member] | Long-term Derivative Positions [Member] | Not Designated as Hedging Instrument [Member]
Derivative Asset, Fair Value			1.1	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting			(1.1)	[2]
Heating Oil [Member] | Long-term Derivative Positions [Member] | Other Deferred Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount
DP&L [Member] | Short-term Derivative Positions [Member] | FTRs [Member]
Derivative Asset, Fair Value	0.2	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting		[2]
DP&L [Member] | Short-term Derivative Positions [Member] | FTRs [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount	0.2
Short-term Derivative Positions [Member] | FTRs [Member]
Derivative Asset, Fair Value	0.2	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting		[2]
Short-term Derivative Positions [Member] | FTRs [Member] | Derivative Instruments Not Designated as Hedging Instruments [Member]
Derivative Asset, Fair Value			0.3	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting				[2]
Short-term Derivative Positions [Member] | FTRs [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount	0.2		0.3
DP&L [Member] | Short-term Derivative Positions [Member] | Forward Power Contracts [Member]
Derivative Asset, Fair Value	0.4	[1]
Derivative Liability, Fair Value	(0.5)	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	(0.3)	[2]
Derivative, Fair Value Counterparty and Collateral, Netting	0.3	[2]
DP&L [Member] | Short-term Derivative Positions [Member] | Forward Power Contracts [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount	0.1
DP&L [Member] | Short-term Derivative Positions [Member] | Forward Power Contracts [Member] | Other Current Liabilities [Member]
Derivative Liability, Fair Value, Not Offset Amount	(0.2)
DP&L [Member] | Long-term Derivative Positions [Member] | Forward Power Contracts [Member]
Derivative Asset, Fair Value	0.4	[1]
Derivative Liability, Fair Value	(0.3)	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	0.1	[2]
Derivative, Fair Value Counterparty and Collateral, Netting	0.1	[2]
DP&L [Member] | Long-term Derivative Positions [Member] | Forward Power Contracts [Member] | Other Deferred Credits [Member]
Derivative Liability, Fair Value, Not Offset Amount	(0.2)
DP&L [Member] | Long-term Derivative Positions [Member] | Forward Power Contracts [Member] | Other Deferred Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount	0.3
Short-term Derivative Positions [Member] | Forward Power Contracts [Member]
Derivative Asset, Fair Value	6.1	[1]
Derivative Liability, Fair Value	(4.5)	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	(0.3)	[2]
Derivative, Fair Value Counterparty and Collateral, Netting	1.3	[2]
Short-term Derivative Positions [Member] | Forward Power Contracts [Member] | Derivative Instruments Not Designated as Hedging Instruments [Member]
Derivative Liability, Fair Value			(0.1)	[1]
Derivative, Fair Value Counterparty and Collateral, Netting				[2]
Short-term Derivative Positions [Member] | Forward Power Contracts [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount	5.8
Short-term Derivative Positions [Member] | Forward Power Contracts [Member] | Other Current Liabilities [Member]
Derivative Liability, Fair Value, Not Offset Amount	(3.2)		(0.1)
Long-term Derivative Positions [Member] | Forward Power Contracts [Member]
Derivative Asset, Fair Value	6.2	[1]
Derivative Liability, Fair Value	(2.2)	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	(0.1)	[2]
Derivative, Fair Value Counterparty and Collateral, Netting	1.1	[2]
Long-term Derivative Positions [Member] | Forward Power Contracts [Member] | Other Deferred Credits [Member]
Derivative Liability, Fair Value, Not Offset Amount	(1.1)
Long-term Derivative Positions [Member] | Forward Power Contracts [Member] | Other Deferred Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount	6.1
Short-term Derivative Positions [Member] | NYMEX-Quality Coal Forwards [Member] | Derivative Instruments Not Designated as Hedging Instruments [Member]
Derivative Asset, Fair Value			14.0	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting			(7.4)	[2]
Short-term Derivative Positions [Member] | NYMEX-Quality Coal Forwards [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount			6.6
Long-term Derivative Positions [Member] | NYMEX-Quality Coal Forwards [Member] | Derivative Instruments Not Designated as Hedging Instruments [Member]
Derivative Asset, Fair Value			23.5	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting			(14.5)	[2]
Long-term Derivative Positions [Member] | NYMEX-Quality Coal Forwards [Member] | Other Deferred Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount			9.0
DP&L [Member] | Short-term Derivative Positions [Member] | NYMEX Coal [Member]
Derivative Asset, Fair Value	12.6	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	6.8	[2]
DP&L [Member] | Short-term Derivative Positions [Member] | NYMEX Coal [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount	5.8
DP&L [Member] | Long-term Derivative Positions [Member] | NYMEX Coal [Member]
Derivative Asset, Fair Value	11.5	[1]
Derivative Liability, Fair Value	(0.5)	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	6.8	[2]
Derivative, Fair Value Counterparty and Collateral, Netting	0.5	[2]
DP&L [Member] | Long-term Derivative Positions [Member] | NYMEX Coal [Member] | Other Deferred Credits [Member]
Derivative Liability, Fair Value, Not Offset Amount
DP&L [Member] | Long-term Derivative Positions [Member] | NYMEX Coal [Member] | Other Deferred Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount	4.7
Short-term Derivative Positions [Member] | NYMEX Coal [Member]
Derivative Asset, Fair Value	12.6	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	(6.8)	[2]
Short-term Derivative Positions [Member] | NYMEX Coal [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount	5.8
Long-term Derivative Positions [Member] | NYMEX Coal [Member]
Derivative Asset, Fair Value	11.5	[1]
Derivative Liability, Fair Value	(0.5)	[1]
Derivative, Fair Value of Derivative Asset Counterparty and Collateral, Netting	6.8	[2]
Derivative, Fair Value Counterparty and Collateral, Netting	0.5	[2]
Long-term Derivative Positions [Member] | NYMEX Coal [Member] | Other Deferred Credits [Member]
Derivative Liability, Fair Value, Not Offset Amount
Long-term Derivative Positions [Member] | NYMEX Coal [Member] | Other Deferred Assets [Member]
Derivative Asset, Fair Value, Not Offset Amount	4.7
Short-term Derivative Positions [Member] | Derivative Instruments Not Designated as Hedging Instruments [Member]
Derivative, Fair Value, Not Offset, Net			14.7	[1]
Derivative, Fair Value Counterparty and Collateral, Netting			7.9	[2]
Derivative, Fair Value, Offset, Net			6.8
DP&L [Member]
Derivative Liability, Fair Value	$ (4.1)

[1] Includes credit valuation adjustment.

[2] Includes counterparty and collateral netting.