Fair Value Measurements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Long Term Debt Range Adjusted To Fair Value at Merger Start	2016
Long Term Debt Range Adjusted To Fair Value At Merger End	2061
Unrealized gains / (losses) on financial instruments, Amount before tax	$ 1.0		$ 0.8
Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss), Net of Tax	(0.7)		0.5
Unrealized gains and immaterial unrealized losses in AOCI, after tax	0.7
Percent of inputs to the fair value of derivative instruments from quoted market prices	98.00%
Gross additions to our existing landfill and asbestos AROs	0.6	1.2
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds	0.6
AvailableForSaleSecuritiesGross Realized Gains Losses Sale Proceeds Net of Tax	(0.4)
DP&L [Member]
Long Term Debt Range Adjusted To Fair Value at Merger Start	2016
Long Term Debt Range Adjusted To Fair Value At Merger End	2061
Unrealized gains and immaterial unrealized losses in AOCI, before tax	1.1		1.1
Unrealized gains and immaterial unrealized losses in AOCI, after tax	(0.7)		0.7
Percent of inputs to the fair value of derivative instruments from quoted market prices	98.00%
Gross additions to our existing landfill and asbestos AROs	0.6	1.2
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds	0.6
AvailableForSaleSecuritiesGross Realized Gains Losses Sale Proceeds Net of Tax	$ 0.4