Consolidated Statements of Comprehensive Income/(Loss) (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	$ (0.1)	$ 0.1	$ 0.2
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	0.0	0.0	(0.2)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	(8.8)	(10.3)	10.3
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	16.7	5.4	(9.5)
Income tax (expense)/benefit on prior service cost related to pension and postretirement activity	0.0	0.0	1.3
Income tax (expense)/benefit on net loss related to pension and postretirement activity	2.4	(1.2)	7.1
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	(0.6)	(0.2)	0.0
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	0.2
Other Comprehensive Income (Loss), Reclassification Adjustment for Sale of Securities Included in Net Income, Tax	0.0	0.0	(0.2)
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	(8.7)	(10.3)	10.5
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	16.4	5.6	(11.5)
Income tax (expense)/benefit on prior service cost related to pension and postretirement activity	0.0	0.0	1.3
Income tax (expense)/benefit on net loss related to pension and postretirement activity	1.1	(1.0)	7.2
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	$ (1.8)	$ (1.9)	$ (1.5)