Benefit Plans (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Amount Billed to Service Company		$ 1,800,000	$ 1,100,000
Defined contribution plan, maximum annual contributions per employee (percent)		85.00%
Employer contributions to defined contribution plan		$ 3,700,000	3,100,000	$ 5,100,000
Accumulated benefit obligation for our defined benefit pension plans		378,700,000	428,300,000
THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Amount Billed to Service Company		$ 1,800,000	1,100,000
Defined contribution plan, maximum annual contributions per employee (percent)		85.00%
Employer contributions to defined contribution plan		$ 3,700,000	3,100,000	5,100,000
Accumulated benefit obligation for our defined benefit pension plans		378,700,000	428,300,000
Defined Benefit Plan, Amount Billed to AES Ohio Generation		$ 3,300,000	700,000
Defined Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan employee vested percentage		100.00%
Defined benefit plan employee vested minimum period, years		5 years
Defined benefit plan, percent forfeited if terminated, other than by death or disability, prior to full vesting (percent)		100.00%
Defined Benefit Plan [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan employee vested percentage		100.00%
Defined benefit plan employee vested minimum period, years		5 years
Defined benefit plan, percent forfeited if terminated, other than by death or disability, prior to full vesting (percent)		100.00%
Management Employees [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan employee vested percentage		100.00%
Defined benefit plan employee vested minimum period, years		3 years
Defined benefit plan, percent forfeited if terminated, other than by death or disability, prior to full vesting (percent)		100.00%
Cash Balance Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan employee vested percentage		100.00%
Defined benefit plan employee vested minimum period, years		3 years
Defined benefit plan, percent forfeited if terminated, other than by death or disability, prior to full vesting (percent)		100.00%
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		$ (34,600,000)	28,100,000
Payment for Pension Benefits		$ 7,500,000	$ 5,000,000	$ 5,000,000
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets		6.25%	6.50%	6.50%
Discount rate for obligations		4.35%	3.66%	4.28%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.66%	4.28%	4.49%
Defined Benefit Plan, Plan Assets, Amount		$ 312,900,000	$ 357,500,000	$ 341,000,000
Service cost		6,100,000	5,700,000	5,700,000
Interest cost		13,800,000	14,200,000	14,700,000
Defined Benefit Plan, Funded (Unfunded) Status of Plan		$ (73,600,000)	(79,400,000)
Defined benefit plan, amortization period for underfunding excess		7 years
Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)		$ (34,600,000)	28,100,000
Payment for Pension Benefits		$ 7,500,000	$ 5,000,000	$ 5,000,000
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets		6.25%	6.50%	6.50%
Discount rate for obligations		4.35%	3.66%	4.28%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		3.66%	4.28%	4.49%
Defined Benefit Plan, Plan Assets, Amount		$ 312,900,000	$ 357,500,000	$ 341,000,000
Service cost		6,100,000	5,700,000	5,700,000
Interest cost		13,800,000	14,200,000	$ 14,700,000
Defined Benefit Plan, Funded (Unfunded) Status of Plan		$ (73,600,000)	(79,400,000)
Defined benefit plan, amortization period for underfunding excess		7 years
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan		$ 9,200,000	12,700,000
Postretirement [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Funded (Unfunded) Status of Plan		$ 9,200,000	$ 12,700,000
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		38.00%
Equity Securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		38.00%
Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase in pension cost due to change in return on assets	$ 3,200,000
Decrease in pension cost due to change in return on assets	(3,200,000)
Decrease in pension cost due to change in discount rate	(100,000)
Increase in pension cost due to change in discount rate	400,000
Scenario, Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase in pension cost due to change in return on assets	3,200,000
Decrease in pension cost due to change in return on assets	(3,200,000)
Decrease in pension cost due to change in discount rate	(100,000)
Increase in pension cost due to change in discount rate	400,000
Scenario, Forecast [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5,400,000
Defined Benefit Plan, Plan Assets, Administration Expense	1,900,000
Scenario, Forecast [Member] | Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5,400,000
Defined Benefit Plan, Plan Assets, Administration Expense	$ 1,900,000
Scenario, Forecast [Member] | SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Allocation Percentage	101.00%
Estimated contribution to the defined benefit plans next year	$ 400,000
Scenario, Forecast [Member] | SERP [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Allocation Percentage	101.00%
Estimated contribution to the defined benefit plans next year	$ 400,000
Non-union Participant [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, period after which participant is fully vested in employer contributions		2 years
Non-union Participant [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, period after which participant is fully vested in employer contributions		2 years
Non-union Participant [Member] | First 1% of Eligible Compensation [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution (percent)		100.00%
Defined contribution plan, employer matching contribution, percent of employees' gross pay (percent)		1.00%
Non-union Participant [Member] | First 1% of Eligible Compensation [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution (percent)		100.00%
Defined contribution plan, employer matching contribution, percent of employees' gross pay (percent)		1.00%
Non-union Participant [Member] | Next 5% of Eligible Compensation [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution (percent)		50.00%
Defined contribution plan, employer matching contribution, percent of employees' gross pay (percent)		5.00%
Non-union Participant [Member] | Next 5% of Eligible Compensation [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution (percent)		50.00%
Defined contribution plan, employer matching contribution, percent of employees' gross pay (percent)		5.00%
Union Participant [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of employees' gross pay (percent)		150.00%
Defined contribution plan, period after which participant is fully vested in employer contributions		3 years
Defined contribution plan, employer matching contribution cap		$ 2,400
Union Participant [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of employees' gross pay (percent)		150.00%
Defined contribution plan, period after which participant is fully vested in employer contributions		3 years
Defined contribution plan, employer matching contribution cap		$ 2,400
Subsequent Event [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits	$ 7,500,000
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	6.25%
Subsequent Event [Member] | Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Payment for Pension Benefits	$ 7,500,000
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	6.25%
Subsequent Event [Member] | Increase in Expected Rate of Return [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in Expected rate of return on plan assets	1.00%
Subsequent Event [Member] | Increase in Expected Rate of Return [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in Expected rate of return on plan assets	1.00%
Subsequent Event [Member] | Decrease in Expected Rate of Return [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in Expected rate of return on plan assets	1.00%
Subsequent Event [Member] | Expected Increase in Discount Rate [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in discount rate for plan assets	25.00%
Subsequent Event [Member] | Expected Increase in Discount Rate [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in discount rate for plan assets	25.00%
Subsequent Event [Member] | Expected Decrease in Discount Rate [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in discount rate for plan assets	25.00%
Subsequent Event [Member] | Expected Decrease in Discount Rate [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in discount rate for plan assets	25.00%
Minimum [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		24.00%
Minimum [Member] | Equity Securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		24.00%
Minimum [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		47.00%
Minimum [Member] | Fixed Income Securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		47.00%
Maximum [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		52.00%
Maximum [Member] | Equity Securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		52.00%
Maximum [Member] | Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		65.00%
Maximum [Member] | Fixed Income Securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		65.00%