Business Segments (Segment Financial Information) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	12 Months Ended
	Oct. 01, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Amortization of intangibles		$ (35.2)	[1]	$ (30.5)	[1]
Goodwill, Impairment Loss	306.3
Total Assets		3,577.8		3,721.5
Utility [Member]
Fixed asset impairment						80.8
Other Reportable Business Segment [Member]
Amortization of intangibles		1.2
Goodwill, Impairment Loss						1,817.2
Fixed asset impairment						(80.8)
Parent Company [Member]
Amortization of intangibles		1.2
Goodwill, Impairment Loss						1,817.2
DP&L [Member]
Intersegment revenues		0.1
Goodwill, Impairment Loss				(306.3)
Income tax expense (benefit)		39.7		18.6		55.1
Successor [Member]
Total revenues		1,763.0		1,636.9		1,668.4
Fuel Costs		304.5		366.7		361.9
Purchased power		592.6		389.0		342.1
Amortization of intangibles		1.2		7.1		95.1
Gross margin		864.7		874.1		869.3
Depreciation and amortization		139.8		132.9		125.4
Goodwill, Impairment Loss		135.8		306.3		1,817.2
Fixed asset impairment		11.5		26.2
Interest expense		126.6		124.0		122.9
Income tax expense (benefit)		18.0		22.3		47.7
Net income (loss)		(74.6)		(222.0)		(1,729.8)
Successor [Member] | Utility [Member]
External customer revenues		1,181.2		1,098.2		1,138.4
Intersegment revenues		487.1		453.3		393.4
Total revenues		1,668.3		1,551.5		1,531.8
Fuel Costs		314.9		362.5		354.9
Purchased power		582.4		381.9		309.5
Gross margin		771.0		807.1		867.4
Depreciation and amortization		144.8		140.2		141.3
Fixed asset impairment				86.0
Interest expense		33.9		37.2		39.1
Income tax expense (benefit)		39.7		18.6		55.1
Net income (loss)		115.0		83.6		91.2
Capital expenditures		114.2		122.1		195.5
Total Assets		3,338.7		3,313.1		3,464.2
Successor [Member] | Competitive Retail [Member]
External customer revenues		533.6		511.6		493.1
Total revenues		533.6		511.6		493.1
Purchased power		491.8		459.7		424.5
Gross margin		41.8		51.9		68.6
Depreciation and amortization		0.8		0.6		0.4
Interest expense		0.5		0.5		0.6
Income tax expense (benefit)		2.0		4.2		18.1
Net income (loss)		3.2		6.6		22.8
Capital expenditures		2.5
Total Assets		94.9		105.0		99.2
Successor [Member] | Other Reportable Business Segment [Member]
External customer revenues		48.2		27.1		36.9
Intersegment revenues		5.5		4.0		3.4
Total revenues		53.7		31.1		40.3
Fuel Costs		(10.4)		4.2		7.0
Purchased power		7.5		1.1		1.5
Amortization of intangibles				7.1		95.1
Gross margin		55.4		18.7		(63.3)
Depreciation and amortization		(5.8)		(7.9)		(16.3)
Goodwill, Impairment Loss		135.8		306.3
Fixed asset impairment		11.5		(59.8)
Interest expense		92.9		86.9		83.9
Income tax expense (benefit)		(23.7)		(0.5)		(25.5)
Net income (loss)		(192.8)		(312.2)		(1,725.4)
Capital expenditures		1.4		2.3		2.6
Total Assets		1,440.1		1,675.8		683.9
Successor [Member] | Adjustments and Eliminations [Member]
Intersegment revenues		(492.6)		(457.3)		(396.8)
Total revenues		(492.6)		(457.3)		(396.8)
Purchased power		(489.1)		(453.7)		(393.4)
Gross margin		(3.5)		(3.6)		(3.4)
Interest expense		(0.7)		(0.6)		(0.7)
Net income (loss)						(118.4)
Total Assets		(1,295.9)		(1,372.4)
Successor [Member] | Parent Company [Member]
External customer revenues		1,763.0		1,636.9		1,668.4
Total revenues		1,763.0		1,636.9		1,668.4
Fuel Costs		304.5		366.7		361.9
Purchased power		592.6		389.0		342.1
Amortization of intangibles				7.1		95.1
Gross margin		864.7		874.1		869.3
Depreciation and amortization		139.8		132.9		125.4
Goodwill, Impairment Loss		135.8		306.3
Fixed asset impairment		11.5		26.2
Interest expense		126.6		124.0		122.9
Income tax expense (benefit)		18.0		22.3		47.7
Net income (loss)		(74.6)		(222.0)		(1,729.8)
Capital expenditures		118.1		124.4		198.1
Total Assets		$ 3,577.8		$ 3,721.5		$ 4,247.3

[1] (c)Consists of various intangible assets including renewable energy credits, emission allowances, and other intangibles, none of which are individually significant.