Fixed-asset Impairment Fixed-asset Impairment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Impairment of Long-Lived Assets Held-for-use	$ 0.0	$ 0.0	$ 235.5	$ 0.0
Killen [Member]
Impairment of Long-Lived Assets Held-for-use			230.8
Peaking Generating Facilities [Member]
Impairment of Long-Lived Assets Held-for-use			4.7
THE DAYTON POWER AND LIGHT COMPANY [Member]
Impairment of Long-Lived Assets Held-for-use	0.0	$ 0.0	857.1	$ 0.0
THE DAYTON POWER AND LIGHT COMPANY [Member] | Stuart [Member]
Impairment of Long-Lived Assets Held-for-use			292.0
THE DAYTON POWER AND LIGHT COMPANY [Member] | Killen [Member]
Impairment of Long-Lived Assets Held-for-use			246.2
THE DAYTON POWER AND LIGHT COMPANY [Member] | Zimmer [Member]
Impairment of Long-Lived Assets Held-for-use			318.9
Level 3 [Member] | Killen [Member]
Property, Plant, and Equipment, Fair Value Disclosure	84.3		84.3
Level 3 [Member] | Peaking Generating Facilities [Member]
Property, Plant, and Equipment, Fair Value Disclosure	5.2		5.2
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Stuart [Member]
Property, Plant, and Equipment, Fair Value Disclosure	164.4		164.4
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Killen [Member]
Property, Plant, and Equipment, Fair Value Disclosure	84.3		84.3
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Zimmer [Member]
Property, Plant, and Equipment, Fair Value Disclosure	$ 111.0		$ 111.0