Fair Value Measurements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 DP&L [Member]	Sep. 30, 2013 DP&L [Member]	Dec. 31, 2012 DP&L [Member]
Long Term Debt Range Adjusted To Fair Value at Merger Start	2016		2028
Long Term Debt Range Adjusted To Fair Value At Merger End	2061		2061
Unrealized gains / (losses) on financial instruments, Amount before tax	$ 0.7	$ 0.9			$ 1.2
Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss), Net of Tax	(0.5)	0.6			0.7
Unrealized gains and immaterial unrealized losses in AOCI, before tax			1.0
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	99.00%			99.00%
Gross additions to our existing landfill and asbestos AROs	1.2
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds	0.3			0.3
AvailableForSaleSecuritiesGross Realized Gains Losses Sale Proceeds Net of Tax	$ 0.2			$ 0.2