Income Taxes (Components of Income Tax Expense) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended						1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	11 Months Ended	12 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2012 DP&L [Member]		Dec. 31, 2011 DP&L [Member]		Dec. 31, 2010 DP&L [Member]		Dec. 31, 2011 Successor [Member]	Dec. 31, 2012 Successor [Member]	Dec. 31, 2011 Successor [Member] Parent Company [Member]	Dec. 31, 2012 Successor [Member] Parent Company [Member]	Nov. 27, 2011 Predecessor [Member]	Dec. 31, 2010 Predecessor [Member]	Nov. 27, 2011 Predecessor [Member] Parent Company [Member]	Dec. 31, 2010 Predecessor [Member] Parent Company [Member]
Federal income tax	$ 50.9	[1]	$ 103.8	[1]	$ 144.2	[1]	$ (2.0)	$ (588.7)			$ 88.4	$ 151.7
State income taxes, net of federal effect	(2.0)		1.4		1.9		0.1	3.5			3.8	2.4
Depreciation of AFUDC - Equity	3.0		(3.2)		(2.2)		(0.3)	(2.4)			(2.9)	(2.2)
Investment tax credit amortized	(2.5)		(2.5)		(2.8)		(0.2)	(0.3)			(2.3)	(2.8)
Section 199 - domestic production deduction	(2.5)		(4.9)		(9.1)			(2.1)			(3.6)	(9.1)
Non-deductible merger costs							0.1				6.0
Non-deductible merger-related compensation	0.6		3.6				3.5	0.6
Non-deductible goodwill impairment								636.0
Derivatives							(0.1)
ESOP			13.6
Income Tax Rate Reconciliation, Deductions, Employee Stock Ownership Plan Dividends			13.6
Compensation on benefits			(5.3)								13.8	0.4
Income not subject to tax							(0.6)
Other, net	7.6	[2]	(2.3)	[2]	3.2	[2]	0.1	1.1			(1.2)	2.6
Total tax expense	55.1		104.2		135.2		0.6	47.7	0.6	47.7	102.0	143.0	102.0	143.0
Federal - Current	52.1		54.9		83.1		0.4	48.6			53.2	84.8
State and Local - Current	1.0		0.9		0.8		0.4	1.2			0.9	1.1
Total Current	53.1		55.8		83.9		0.8	49.8			54.1	85.9
Federal - Deferred	4.7		47.1		50.1		(0.2)	(4.9)			43.2	55.9
State and Local - Deferred	(2.7)		1.3		1.2			2.8			4.7	1.2
Deferred income taxes	2.0		48.4		51.3		0.1	(4.2)			65.5	59.9
Total Deferred							$ (0.2)	$ (2.1)			$ 47.9	$ 57.1

[1] The statutory tax rate of 35% was applied to pre-tax earnings.

[2] Includes expense of $7.6 million and benefits of $2.4 million and $0.3 million in 2012, 2011 and 2010, respectively, of income tax related to adjustments from prior years.