Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unrealized Gain (Loss) on Investments	$ 0.5	$ (1.5)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Gain (Loss) on Investments	0.5	(1.5)
Entity Information [Line Items]
Unrealized Gain (Loss) on Investments	0.5	(1.5)
Fair Value, Inputs, Level 1 [Member]
Total Liabilities	0.0	0.0
Fair Value, Inputs, Level 2 [Member]
Total Liabilities	1,706.2	1,376.4
Fair Value, Inputs, Level 3 [Member]
Total Liabilities	16.8	17.0
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	0.5	(1.5)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Gain (Loss) on Investments	0.5	(1.5)
Entity Information [Line Items]
Unrealized Gain (Loss) on Investments	0.5	$ (1.5)
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	909.9
THE DAYTON POWER AND LIGHT COMPANY [Member] | Fair Value, Inputs, Level 3 [Member]
Total Liabilities	$ 16.8