Pension and Postretirement Benefits (Other Changes in Plan Assets and Benefit Obligation Recognized in Accumulated Other Comprehensive Income, Regulatory Assets And Regulatory Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Nov. 27, 2011	Dec. 31, 2010
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	$ 5.5		$ (38.7)	$ 1.9
Prior service cost / (credit)			(2.2)
Reversal of amortization item, Net actuarial (gain) / loss	(5.0)	(0.4)	(7.6)	(7.2)
Reversal of amortization item, Prior service cost / (credit)	(1.5)	(0.1)	(2.0)	(3.7)
Total recognized in Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	(1.0)	(0.5)	(50.5)	(9.0)
Total recognized in net periodic benefit cost and Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	6.3	(0.5)	(43.4)	2.0
Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	5.2	22.8		1.9
Prior service cost / (credit)		7.1
Reversal of amortization item, Net actuarial (gain) / loss	(9.4)	(8.0)		(7.2)
Reversal of amortization item, Prior service cost / (credit)	(2.8)	(2.0)		(3.7)
Total recognized in Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	(7.0)	19.9		(9.0)
Total recognized in net periodic benefit cost and Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	6.0	27.5		2.0
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	1.0		0.2	(1.9)
Prior service cost / (credit)		0.1	(0.1)
Reversal of amortization item, Net actuarial (gain) / loss	0.7		1.0	1.1
Reversal of amortization item, Prior service cost / (credit)			(0.1)	(0.1)
Transition (asset) / obligation		(0.1)
Total recognized in Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	1.7		1.0	(0.9)
Total recognized in net periodic benefit cost and Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	1.8		0.8	(0.9)
Postretirement [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	1.1	(1.3)		(1.9)
Reversal of amortization item, Net actuarial (gain) / loss	0.9	1.2		1.1
Reversal of amortization item, Prior service cost / (credit)	(0.1)	(0.1)		(0.1)
Total recognized in Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	1.9	(0.2)		(0.9)
Total recognized in net periodic benefit cost and Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	$ 1.8	$ (0.4)		$ (0.9)