Consolidated Statements of Comprehensive Income/(Loss) (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	$ 0.2	$ (0.1)	$ 0.2	$ 0.7
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(0.1)	(0.2)	(0.7)	(0.2)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	(1.0)	(3.3)	12.4	(10.0)
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(1.5)	(0.8)	(7.4)	(2.1)
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity				0.3
THE DAYTON POWER AND LIGHT COMPANY [Member]
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	0.2	0.1	0.2	0.9
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(0.1)	(0.2)	(0.2)	(0.7)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	(0.7)	0.1	9.9
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(1.9)	(0.9)	(6.7)	(2.2)
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	$ (0.3)	$ (0.5)	$ (1.0)	$ (1.5)