Property, Plant and Equipment (Changes in the Liability for Transmission and Distribution Asset Removal Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Changes in Liability for Transmission and Distribution Asset Removal Costs [Roll Forward]
Balance at January 1	$ 138.8	$ 143.6
Additions	17.0	15.6
Settlements	(10.6)	(20.4)
Balance at December 31	145.2	138.8
THE DAYTON POWER AND LIGHT COMPANY [Member]
Changes in Liability for Transmission and Distribution Asset Removal Costs [Roll Forward]
Balance at January 1	138.8	143.6
Additions	17.0	15.6
Settlements	(10.6)	(20.4)
Balance at December 31	$ 145.2	$ 138.8