Consolidated Statements of Comprehensive Income/(Loss) (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	$ 1.0	$ 0.1	$ 0.9	$ (0.2)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(0.5)		(0.6)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	(6.0)	7.4	(6.7)	3.3
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(1.0)		(1.4)	0.9
Income tax (expense)/benefit on prior service cost related to pension and postretirement activity	(0.5)	(0.4)
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	1.0		0.9	(0.2)
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	(0.5)		(0.6)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	(1.7)		(0.2)	0.8
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(1.0)		(1.3)	(0.6)
Income tax (expense)/benefit on prior service cost related to pension and postretirement activity			$ (1.0)	$ (1.1)