Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unrealized Gain (Loss) on Investments	$ (1.7)	$ 0.7	$ 0.6
Fair Value, Inputs, Level 1 [Member]
Total Liabilities	0.0	0.0
Fair Value, Inputs, Level 2 [Member]
Total Liabilities	1,376.4	1,502.5
Fair Value, Inputs, Level 3 [Member]
Total Liabilities	17.0	17.2
THE DAYTON POWER AND LIGHT COMPANY [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unrealized Gain (Loss) on Investments	(1.7)	$ 0.7	$ 0.6
THE DAYTON POWER AND LIGHT COMPANY [Member] | Fair Value, Inputs, Level 1 [Member]
Total Liabilities	0.0
THE DAYTON POWER AND LIGHT COMPANY [Member] | Fair Value, Inputs, Level 2 [Member]
Total Liabilities	610.9
THE DAYTON POWER AND LIGHT COMPANY [Member] | Fair Value, Inputs, Level 3 [Member]
Total Liabilities	$ 17.0