Benefit Plans (Pension and Postretirement Benefit Plans' Obligations and Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	$ 9.6	$ 98.0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Noncurrent liabilities	(37.7)	(41.8)
THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(7.2)
Noncurrent liabilities	(37.7)	(41.8)
Postretirement [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Funded (Unfunded) Status of Plan		7.0
Postretirement [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Funded (Unfunded) Status of Plan	7.2	7.0
Pension [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1	309.0	416.2
Service cost	3.0	4.9	$ 4.5
Interest cost	15.8	9.6	8.2
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	9.6	(98.0)
Benefit obligation at December 31	298.6	309.0	416.2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at January 1	274.4	363.5
Actual return / (loss) on plan assets	26.5	(73.1)
Contributions to plan assets	7.7	7.7
Fair value of plan assets at December 31	268.4	274.4	363.5
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(30.2)	(34.6)
Current liabilities	(0.2)	(0.2)
Noncurrent liabilities	(30.0)	(34.4)
Net asset / (liability) at December 31	(30.2)	(34.6)
Prior service cost	7.7	7.3
Net actuarial loss	78.7	78.6
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax	86.4	85.9
Defined Benefit Plan, Plan Assets, Benefits Paid	40.2	23.7
Defined Benefit Plan, Benefit Obligation, Benefits Paid	40.2	23.7
Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1	309.0	416.2
Service cost	3.0	4.9	4.5
Interest cost	15.8	9.6	8.2
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	9.6	(98.0)
Benefit obligation at December 31	298.6	309.0	416.2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at January 1	274.4	363.5
Actual return / (loss) on plan assets	26.5	(73.1)
Contributions to plan assets	7.7	7.7
Fair value of plan assets at December 31	268.4	274.4	$ 363.5
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(30.2)	(34.6)
Current liabilities	(0.2)	(0.2)
Noncurrent liabilities	(30.0)	(34.4)
Net asset / (liability) at December 31	(30.2)	(34.6)
Prior service cost	7.6	7.3
Net actuarial loss	102.3	102.7
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax	109.9	110.0
Defined Benefit Plan, Plan Assets, Benefits Paid	40.2	23.7
Defined Benefit Plan, Benefit Obligation, Benefits Paid	40.2	23.7
Regulatory Asset [Member] | Pension [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax	60.7	62.0
Regulatory Asset [Member] | Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax	60.7	62.0
Accumulated Other Comprehensive Income/(Loss) [Member] | Pension [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax	25.7	23.9
Accumulated Other Comprehensive Income/(Loss) [Member] | Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Accumulated other comprehensive income, regulatory assets and regulatory liabilities, pre-tax	$ 49.2	$ 48.0