Consolidated Statements of Comprehensive Income/(Loss) (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	$ (0.2)	$ (0.7)
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(9.5)	(2.3)	0.5
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity		0.3
Successor [Member]
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	0.2	0.6	(0.2)
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	10.3	(10.6)	1.4
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(9.5)	(2.3)	0.4
Income tax (expense)/benefit on net loss related to pension and postretirement activity	8.3	(2.7)	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	0.2	0.9	(0.2)
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	10.5	(0.6)	1.6
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	(11.5)	(2.5)	0.5
Income tax (expense)/benefit on prior service cost related to pension and postretirement activity		(0.2)	(0.5)
Income tax (expense)/benefit on net loss related to pension and postretirement activity	6.9	(1.9)	0.8
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity		$ (1.9)	$ (1.5)