Consolidated Statements of Comprehensive Income/(Loss) (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	$ 0.2	$ (0.1)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(0.1)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	7.0	(1.1)
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(3.1)	(0.1)
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	(0.2)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(0.1)	(0.1)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	7.0	1.4
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(3.2)	(0.2)
Income tax (expense)/benefit on prior service cost related to pension and postretirement activity		(0.5)
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	$ (0.4)