Consolidated Statements of Comprehensive Income/(Loss) (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	$ (0.1)	$ (0.1)	$ 0.7	$ (0.3)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(0.2)		(0.7)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	(3.3)	(0.3)	(10.0)	3.4
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(0.8)		(2.1)	0.7
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	0.1	(0.1)	0.9	(0.3)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(0.2)		(0.7)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	0.1	1.3		2.2
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(0.9)	0.1	(2.2)	0.7
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	$ (0.5)	$ (0.6)	$ (1.5)	$ (1.7)