Pension and Postretirement Benefits (Pension and Postretirement Benefit Plans' Obligations and Assets) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2011	Nov. 27, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at December 31			$ 361.4
Noncurrent liabilities	(47.5)		(61.6)	(47.5)
DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at December 31			361.4
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at January 1	365.0	333.8	365.2	333.8
Service cost	0.5	4.5	6.2		4.8
Interest cost	1.5	15.5	17.3		17.7
Plan amendments		7.2
Actuarial (gain) / loss		21.6	29.1
Benefits paid	(1.8)	(17.6)	(22.2)
Benefit obligation at December 31	365.2	365.0	395.6	365.2	333.8
Fair value of plan assets at January 1	335.8	291.8	335.9	291.8
Actual return / (loss) on plan assets	1.9	21.2	46.2
Contributions to plan assets		40.4	1.5
Fair value of plan assets at December 31	335.9	335.8	361.4	335.9	291.8
Funded Status of Plan	(29.3)	(29.2)	(34.2)	(29.3)
Current liabilities	(1.3)		(0.4)	(1.3)
Noncurrent liabilities	(27.9)		(33.8)	(27.9)
Net asset / (liability) at December 31	(29.2)		(34.2)	(29.2)
Prior service cost / (credit)			10.3	12.5
Net actuarial loss / (gain)			79.9	78.7
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			90.2	91.2
Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at January 1		333.8	365.2	333.8
Service cost			6.2	5.0	4.8
Interest cost			17.3	17.0	17.7
Plan amendments				7.2
Actuarial (gain) / loss			29.1	21.6
Benefits paid			(22.2)	(19.4)
Benefit obligation at December 31	365.2		395.6	365.2	333.8
Fair value of plan assets at January 1		291.8	335.9	291.8
Actual return / (loss) on plan assets			46.2	23.1
Contributions to plan assets			1.5	40.4
Fair value of plan assets at December 31	335.9		361.4	335.9	291.8
Funded Status of Plan	(29.3)		(34.2)	(29.3)
Current liabilities	(1.3)		(0.4)	(1.3)
Noncurrent liabilities	(27.9)		(33.8)	(27.9)
Net asset / (liability) at December 31	(29.2)		(34.2)	(29.2)
Prior service cost / (credit)			19.0	21.9
Net actuarial loss / (gain)			136.1	140.2
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			155.1	162.1
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at January 1	21.9	23.7	21.7	23.7
Service cost		0.1	0.1		0.1
Interest cost	0.1	0.9	0.9		1.2
Actuarial (gain) / loss	(0.1)	(1.3)	1.2
Benefits paid	(0.2)	(1.8)	(1.7)
Medicare Part D Reimbursement		0.3	0.2
Benefit obligation at December 31	21.7	21.9	22.4	21.7	23.7
Fair value of plan assets at January 1	4.5	4.8	4.5	4.8
Actual return / (loss) on plan assets		0.2	0.2
Contributions to plan assets	0.2	1.3	1.2
Fair value of plan assets at December 31	4.5	4.5	4.2	4.5	4.8
Funded Status of Plan	(17.2)	(17.4)	(18.2)	(17.2)
Current liabilities	(0.6)		(0.6)	(0.6)
Noncurrent liabilities	(16.6)		(17.6)	(16.6)
Net asset / (liability) at December 31	(17.2)		(18.2)	(17.2)
Prior service cost / (credit)			0.5	0.7
Net actuarial loss / (gain)			(4.5)	(6.4)
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			(4.0)	(5.7)
Postretirement [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at January 1		23.7	21.7	23.7
Service cost			0.1	0.1	0.1
Interest cost			0.9	1.0	1.2
Actuarial (gain) / loss			1.2	(1.3)
Benefits paid			(1.7)	(2.0)
Medicare Part D Reimbursement			0.2	0.2
Benefit obligation at December 31	21.7		22.4	21.7	23.7
Fair value of plan assets at January 1		4.8	4.5	4.8
Actual return / (loss) on plan assets			0.2	0.2
Contributions to plan assets			1.2	1.5
Fair value of plan assets at December 31	4.5		4.2	4.5	4.8
Funded Status of Plan	(17.2)		(18.2)	(17.2)
Current liabilities	(0.6)		(0.6)	(0.6)
Noncurrent liabilities	(16.6)		(17.6)	(16.6)
Net asset / (liability) at December 31	(17.2)		(18.2)	(17.2)
Prior service cost / (credit)			0.8	0.9
Net actuarial loss / (gain)			(5.7)	(7.7)
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			(4.9)	(6.8)
Regulatory Asset [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			88.0	91.2
Regulatory Asset [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			88.0	91.1
Regulatory Asset [Member] | Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			0.5	0.5
Regulatory Asset [Member] | Postretirement [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			0.5	1.0
Regulatory Liability [Member] | Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			(5.0)	(6.2)
Regulatory Liability [Member] | Postretirement [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			(5.0)	(6.6)
Accumulated Other Comprehensive Income/(Loss) [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			2.2
Accumulated Other Comprehensive Income/(Loss) [Member] | Pension [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			67.1	71.0
Accumulated Other Comprehensive Income/(Loss) [Member] | Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			0.5
Accumulated Other Comprehensive Income/(Loss) [Member] | Postretirement [Member] | DP&L [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax			$ (0.4)	$ (1.2)