Condensed Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	$ 0.0	$ 0.0	$ 0.0	$ (0.1)
Income tax (expense) benefit on reclassification to earnings	0.0	0.0	0.0	0.0
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	(0.6)	4.7	(3.4)	7.1
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	0.0	5.9	(0.5)	10.7
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), Tax	0.0	0.0	0.2	0.0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Tax	0.0	0.0	0.7	0.0
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	0.0	0.0	(0.5)	(0.2)
THE DAYTON POWER AND LIGHT COMPANY [Member]
Income tax (expense)/benefit on unrealized gains (losses) related to available-for-sale securities	0.0	0.0	0.0	(0.1)
Income tax (expense) benefit on reclassification to earnings	0.0	0.0	0.0	0.0
Income tax (expense)/benefit on unrealized gains (losses) related to derivative activity	(0.6)	4.7	(3.4)	(7.0)
Income tax (expense)/benefit on reclassification of earnings related to derivative activity	0.0	5.9	(0.5)	10.7
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), Tax	0.0	0.0	0.6	0.0
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized Gain (Loss) Arising During Period, Tax	0.0	0.0	0.2	0.0
Income tax (expense)/benefit on reclassification of earnings related to pension and postretirement activity	$ (0.3)	$ (0.4)	$ (1.6)	$ (1.2)