Consolidated Statements of Comprehensive Income/(Loss) (Parenthetical) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities			$ (0.2)	$ 0
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity			3.3	5.4
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity			0.7	(1.3)
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity			0	(0.8)
Successor [Member]
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	0.1
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	7.4
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	0
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	0
Predecessor [Member]
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities		0
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity		6.0
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity		(1.0)
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	(0.9)	(0.2)	(1.4)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	0	0.3	0.8	0.5
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	0	(0.3)	(0.6)	(0.6)
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	$ (0.4)	$ (0.1)	$ (1.1)	$ (0.1)