Income Taxes (Components of Income Tax Expense) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accrual (settlement) for open tax years	$ (6.6)		$ (8.8)
DP&L [Member]
Federal income tax	53.8		35.5		50.9
State income taxes, net of federal effect	1.2		0.3		(2.0)
Depreciation of AFUDC - Equity	(2.7)		(2.5)		3.0
Investment tax credit amortized	(2.5)		(2.5)		(2.5)
Section 199 - domestic production deduction	(4.6)		(4.1)		(2.5)
Non-deductible merger costs					0.6
Other, net	1.1		0.7		7.6
Total tax expense	39.7		18.6		55.1
Federal - Current	34.1		38.6		52.1
State and Local - Current	0.5		(0.1)		1.0
Total Current	34.6		38.5		53.1
Federal - Deferred	4.1		(20.4)		4.7
State and Local - Deferred	1.0		0.5		(2.7)
Total Deferred	5.1		(19.9)		2.0
Successor [Member]
Federal income tax	(19.8)		(69.9)		(588.7)
State income taxes, net of federal effect	1.2		1.7		3.5
Depreciation of AFUDC - Equity	(3.4)		(3.2)		(2.4)
Investment tax credit amortized	(0.5)		(0.5)		(0.3)
Section 199 - domestic production deduction	(1.1)		(4.1)		(2.1)
Non-deductible merger-related compensation					0.6
Non-deductible goodwill impairment	47.5		107.2		636.0
Accrual (settlement) for open tax years	(6.6)		(8.8)		(0.1)
Other, net	0.7		(0.1)		1.2
Total tax expense	18.0		22.3		47.7
Federal - Current	(0.1)	[1]	1.8	[1]	48.6	[1]
State and Local - Current	0.9		0.7		1.2
Total Current	0.8		2.5		49.8
Federal - Deferred	16.6		18.1		(4.9)
State and Local - Deferred	0.6		1.7		2.8
Deferred income taxes	17.7		24.0		(4.2)
Total Deferred	17.2		19.8		(2.1)
Successor [Member] | Parent Company [Member]
Total tax expense	$ 18.0		$ 22.3		$ 47.7

[1] (b)Includes expense of $0.4 million, $0.0 million and benefits of $1.2 million in the years ended December 31, 2014 2013, and 2012, respectively, of income tax related to adjustments from prior years.