Benefit Plans (Net Periodic Benefit Cost (Income)) (Details) - Pension [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Service cost	$ 2.5	$ 3.0	$ 4.9
Interest cost	14.6	15.8	9.6
Expected return on assets	(14.8)	(17.6)	(15.8)
Actuarial gain / (loss)	2.1	0.6	5.5
Prior service cost	1.0	1.0	1.1
Net Periodic benefit cost / (income) before adjustments	$ 5.4	$ 2.8	$ 5.3
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	5.14%	5.41%	2.83%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	5.15%	5.40%	4.60%
THE DAYTON POWER AND LIGHT COMPANY [Member]
Service cost	$ 2.5	$ 3.0	$ 4.9
Interest cost	14.6	15.8	9.6
Expected return on assets	(14.8)	(17.6)	(15.8)
Actuarial gain / (loss)	3.9	1.1	7.7
Prior service cost	1.0	1.1	1.2
Net Periodic benefit cost / (income) before adjustments	$ 7.2	$ 3.4	$ 7.6
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	5.14%	5.41%	2.83%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	5.15%	5.40%	4.60%