Benefit Plans (Fair Value Measurements for Postretirement Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 345.4	$ 371.7
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.8	3.3	$ 3.7
Postretirement [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.8	3.3	$ 3.7
JP Morgan Core Bond Fund [Member] | Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.8	3.3
JP Morgan Core Bond Fund [Member] | Postretirement [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.8	3.2
Level 1 [Member] | JP Morgan Core Bond Fund [Member] | Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.8	3.3
Level 1 [Member] | JP Morgan Core Bond Fund [Member] | Postretirement [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2.8	$ 3.2