Derivative Instruments and Hedging Activities (Fair Values of Derivative Instruments Designated as Hedging Instruments) (Details) (Not Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | DP&L [Member]
Derivative Liability, Fair Value		$ (0.7)
Derivative, Fair Value, Net		0.1
Derivative, Fair Value, Offset, Net		(0.6)
Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value	4.9	2.7
Derivative, Fair Value, Net	0.7	1.2
Derivative, Fair Value, Offset, Net	(4.2)	(1.5)
Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | DP&L [Member]
Derivative Asset, Fair Value	4.9	2.8
Derivative, Fair Value, Net	0.7	1.3
Derivative, Fair Value, Offset, Net	(4.2)	(1.5)
Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative Liability, Fair Value	(6.6)	(4.1)
Derivative, Fair Value, Net	0.1	0.6
Derivative, Collateral, net	(2.3)	(2.0)
Derivative, Fair Value, Offset, Net	(4.2)	(1.5)
Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | DP&L [Member]
Derivative Liability, Fair Value	(6.6)	(2.7)
Derivative, Fair Value, Net	0.1	0.7
Derivative, Collateral, net	(2.3)	(0.5)
Derivative, Fair Value, Offset, Net	(4.2)	(1.5)
Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member]
Derivative Liability, Fair Value	(1.3)	(0.8)
Derivative, Fair Value, Net		0.1
Derivative, Collateral, net	(1.0)	(0.1)
Derivative, Fair Value, Offset, Net	(0.3)	(0.6)
Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | DP&L [Member]
Derivative Liability, Fair Value	(1.3)
Derivative, Collateral, net	(1.0)
Derivative, Fair Value, Offset, Net	(0.3)
Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member]
Derivative Asset, Fair Value	5.0	3.6
Derivative, Fair Value, Net	4.7	3.0
Derivative, Fair Value, Offset, Net	(0.3)	(0.6)
Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | DP&L [Member]
Derivative Asset, Fair Value	5.0	3.6
Derivative, Fair Value, Net	4.7	3.0
Derivative, Fair Value, Offset, Net	$ (0.3)	$ (0.6)