Pension and Postretirement Benefits (Estimated Amounts that will be Amortized from Accumulated Other Comprehensive Income, Regulatory Assets And Regulatory Liabilities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	$ 4.9
Prior service cost / (credit)	1.5
Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	9.3
Prior service cost / (credit)	2.8
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	(0.5)
Postretirement [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	(0.7)
Prior service cost / (credit)	$ 0.1