Benefit Plans (Net Periodic Benefit Cost (Income)) (Details) - Pension [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Service cost	$ 4.9	$ 4.5	$ 3.7
Interest cost	9.6	8.2	11.8
Expected return on assets	(15.8)	(15.0)	(18.6)
Actuarial gain / (loss)	5.5	9.0	1.0
Prior service cost	1.1	0.9	6.1
Net Periodic benefit cost / (income) before adjustments	$ 5.3	$ 7.6	$ 4.0
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	2.83%	2.44%	3.33%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	4.60%	4.55%	5.60%
THE DAYTON POWER AND LIGHT COMPANY [Member]
Service cost	$ 4.9	$ 4.5	$ 3.7
Interest cost	9.6	8.2	11.8
Expected return on assets	(15.8)	(15.0)	(18.6)
Actuarial gain / (loss)	7.7	11.4	8.7
Prior service cost	1.2	1.1	1.3
Net Periodic benefit cost / (income) before adjustments	$ 7.6	$ 10.2	$ 6.9
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate	2.83%	2.44%	3.33%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	4.60%	4.55%	5.60%