Derivative Instruments and Hedging Activities (Fair Values of Derivative Instruments Not Designated as Hedging Instruments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Derivative Liability, Fair Value	$ (13.2)
Derivative, Fair Value, Net	1.5	[1]	(7.4)	[1]
DP&L [Member]
Derivative Liability, Fair Value	(11.7)
Short-term Derivative Positions [Member]
Derivative Asset, Fair Value	2.7
Derivative, Fair Value, Net	(1.3)	[1]	(3.0)	[1]
Fair Value Frozen	7.2
Short-term Derivative Positions [Member] | DP&L [Member]
Derivative, Fair Value, Net	0.2	[1]	(6.3)	[1]
Long-term Derivative Positions [Member]
Derivative Asset, Fair Value	3.6
Derivative, Fair Value, Net	2.8	[1]	(4.4)	[1]
Fair Value Frozen	1.0
Long-term Derivative Positions [Member] | DP&L [Member]
Derivative, Fair Value, Net	2.9	[1]	(6.0)	[1]
Not Designated as Hedging Instrument [Member] | DP&L [Member]
Derivative, Fair Value, Net	3.1	[1]	(12.3)	[1]
FTRs [Member] | Other Prepayments and Current Assets [Member] | Short-term Derivative Positions [Member]
Derivative Asset, Fair Value			0.1	[1]
FTRs [Member] | Other Prepayments and Current Assets [Member] | Short-term Derivative Positions [Member] | DP&L [Member]
Derivative Asset, Fair Value			0.1	[1]
FTRs [Member] | Other Current Liabilities [Member] | Short-term Derivative Positions [Member]
Derivative Liability, Fair Value	(0.1)	[1]
Forward Power Contracts [Member] | Other Prepayments and Current Assets [Member] | Short-term Derivative Positions [Member]
Derivative Asset, Fair Value	2.7	[1]	9.9	[1]
Forward Power Contracts [Member] | Other Deferred Credits [Member] | Long-term Derivative Positions [Member]
Derivative Liability, Fair Value	(0.8)	[1]	(4.0)	[1]
Forward Power Contracts [Member] | Other Current Liabilities [Member] | Short-term Derivative Positions [Member]
Derivative Liability, Fair Value	(4.1)	[1]	(6.5)	[1]
Forward Power Contracts [Member] | Other Deferred Assets [Member] | Long-term Derivative Positions [Member]
Derivative Asset, Fair Value			5.8	[1]
NYMEX-Quality Coal Forwards [Member] | Other Deferred Credits [Member] | Long-term Derivative Positions [Member]
Derivative Liability, Fair Value			(6.2)	[1]
NYMEX-Quality Coal Forwards [Member] | Other Current Liabilities [Member] | Short-term Derivative Positions [Member]
Derivative Liability, Fair Value			(8.3)	[1]
Futures [Member] | Other Prepayments and Current Assets [Member] | Short-term Derivative Positions [Member]
Derivative Asset, Fair Value			1.8	[1]
Forward Power Contracts [Member] | Other Deferred Assets [Member] | Long-term Derivative Positions [Member]
Derivative Asset, Fair Value	3.6	[1]
Heating Oil [Member] | Other Prepayments and Current Assets [Member] | Short-term Derivative Positions [Member]
Derivative Asset, Fair Value	0.2	[1]
NYMEX Coal [Member] | Other Deferred Credits [Member] | Long-term Derivative Positions [Member] | DP&L [Member]
Derivative Liability, Fair Value			(6.2)	[1]
NYMEX Coal [Member] | Other Current Liabilities [Member] | Short-term Derivative Positions [Member] | DP&L [Member]
Derivative Liability, Fair Value			(8.3)	[1]
Heating Oil [Member] | Other Prepayments and Current Assets [Member] | Short-term Derivative Positions [Member] | DP&L [Member]
Derivative Asset, Fair Value			1.8	[1]
Heating Oil [Member] | Heating Oil [Member] | Other Prepayments and Current Assets [Member] | Short-term Derivative Positions [Member] | DP&L [Member]
Derivative Asset, Fair Value	0.2	[1]
FTR's [Member] | FTRs [Member] | Other Current Liabilities [Member] | Short-term Derivative Positions [Member] | DP&L [Member]
Derivative Liability, Fair Value	(0.1)	[1]
Forward Power Contracts [Member] | Other Prepayments and Current Assets [Member] | Short-term Derivative Positions [Member] | DP&L [Member]
Derivative Asset, Fair Value			1.0	[1]
Forward Power Contracts [Member] | Other Deferred Credits [Member] | Long-term Derivative Positions [Member] | DP&L [Member]
Derivative Liability, Fair Value			(1.3)	[1]
Forward Power Contracts [Member] | Other Current Liabilities [Member] | Short-term Derivative Positions [Member] | DP&L [Member]
Derivative Liability, Fair Value			(0.9)	[1]
Forward Power Contracts [Member] | Other Deferred Assets [Member] | Long-term Derivative Positions [Member] | DP&L [Member]
Derivative Asset, Fair Value			1.5	[1]
Forward Power Contracts [Member] | Forward Power Contracts [Member] | Other Prepayments and Current Assets [Member] | Short-term Derivative Positions [Member] | DP&L [Member]
Derivative Asset, Fair Value	2.8	[1]
Forward Power Contracts [Member] | Forward Power Contracts [Member] | Other Deferred Credits [Member] | Long-term Derivative Positions [Member] | DP&L [Member]
Derivative Liability, Fair Value	(0.7)	[1]
Forward Power Contracts [Member] | Forward Power Contracts [Member] | Other Current Liabilities [Member] | Short-term Derivative Positions [Member] | DP&L [Member]
Derivative Liability, Fair Value	(2.7)	[1]
Forward Power Contracts [Member] | Forward Power Contracts [Member] | Other Deferred Assets [Member] | Long-term Derivative Positions [Member] | DP&L [Member]
Derivative Asset, Fair Value	$ 3.6	[1]

[1] Includes credit valuation adjustment