Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Jointly Owned Utility Plant Interests [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	$ 0.0	$ 5.1	$ 0.0
Estimated costs of removal	145.2	138.8	143.6
Property, Plant and Equipment [Line Items]
Proceeds from Sale of Property, Plant, and Equipment	0.0	5.1	0.0
THE DAYTON POWER AND LIGHT COMPANY [Member]
Jointly Owned Utility Plant Interests [Line Items]
Estimated costs of removal	$ 145.2	$ 138.8	$ 143.6