Benefit Plans (Net Periodic Benefit Cost (Income)) (Details) - Pension [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Service cost	$ 3.0	$ 4.9	$ 4.5
Interest cost	15.8	9.6	8.2
Expected return on assets	(17.6)	(15.8)	(15.0)
Actuarial gain / (loss)	0.6	5.5	9.0
Prior service cost	1.0	1.1	0.9
Net Periodic benefit cost / (income) before adjustments	$ 2.8	$ 5.3	$ 7.6
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	5.41%	2.83%	2.44%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	5.40%	4.60%	4.55%
THE DAYTON POWER AND LIGHT COMPANY [Member]
Service cost	$ 3.0	$ 4.9	$ 4.5
Interest cost	15.8	9.6	8.2
Expected return on assets	(17.6)	(15.8)	(15.0)
Actuarial gain / (loss)	1.1	7.7	11.4
Prior service cost	1.1	1.2	1.1
Net Periodic benefit cost / (income) before adjustments	$ 3.4	$ 7.6	$ 10.2
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	5.41%	2.83%	2.44%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	5.40%	4.60%	4.55%