Consolidated Statements of Comprehensive Income/(Loss) (Parenthetical) (USD $) In Millions, unless otherwise specified	1 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2011	Nov. 27, 2011	Dec. 31, 2012	Dec. 31, 2010	Dec. 31, 2012 THE DAYTON POWER AND LIGHT COMPANY [Member]	Dec. 31, 2011 THE DAYTON POWER AND LIGHT COMPANY [Member]	Dec. 31, 2010 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)	$ (0.2)	$ 4.3	$ 0.6
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	0.3	31.2	1.4	(6.6)	1.6	0.5	0.2
Income tax (expense)/benefit on reclassification of earnings related to derivative activity		(0.3)	0.4	2.0	0.5	0.1	(0.5)
Income tax (expense)/benefit on prior service cost related to pension and postretirement activity	0.2			(3.7)	(0.5)	(0.4)	(0.4)
Income tax (expense)/benefit on net loss related to pension and postretirement activity	(0.2)	(0.7)	1.0	4.0	0.8	5.4	(0.1)
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity		$ 1.5		$ (1.3)	$ (1.5)	$ (1.5)	$ (0.5)