Benefit Plans (Narrative) (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, non-union employee eligibility threshold (hours)			160 hours
Defined contribution plan, union employee eligibility threshold (days)			30 days
Defined contribution plan, maximum annual contributions per employee (percent)			85.00%
Employer contributions to defined contribution plan			$ 4,800,000	$ 4,700,000	$ 4,800,000
Accumulated benefit obligation for our defined benefit pension plans			$ 401,200,000	$ 431,000,000
Funded status of defined benefit pension plan				112.54%
Change in assumed health care cost trend rate (percent)			1.00%
THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, non-union employee eligibility threshold (hours)			160 hours
Defined contribution plan, union employee eligibility threshold (days)			30 years
Defined contribution plan, maximum annual contributions per employee (percent)			85.00%
Employer contributions to defined contribution plan			$ 4,800,000	$ 4,700,000	4,800,000
Accumulated benefit obligation for our defined benefit pension plans			401,200,000	$ 431,000,000
Funded status of defined benefit pension plan				112.54%
Defined Benefit Plan, Fair Value of Plan Assets, Other Investments			53,000,000	$ 49,500,000
Defined Benefit Plan, Fair Value of Plan Assets			$ 345,400,000	371,700,000
Change in assumed health care cost trend rate (percent)			1.00%
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%
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%
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%
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension Contributions			$ 5,000,000	$ 0	$ 0
Expected rate of return on plan assets			6.50%	6.75%	6.75%
Discount rate for obligations			4.49%	4.02%	4.86%
Discount rate			4.02%	4.86%	4.04%
Defined Benefit Plan, Fair Value of Plan Assets, Other Investments			$ 53,000,000	$ 49,500,000
Defined Benefit Plan, Fair Value of Plan Assets			345,400,000	371,700,000	$ 349,100,000
Service cost			7,100,000	5,900,000	7,200,000
Interest cost			17,300,000	17,500,000	15,600,000
Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension Contributions			$ 5,000,000	$ 0	$ 0
Expected rate of return on plan assets			6.50%	6.75%	6.75%
Discount rate for obligations			4.49%	4.02%	4.86%
Discount rate			4.02%	4.86%	4.04%
Defined Benefit Plan, Fair Value of Plan Assets			$ 345,400,000	$ 371,700,000	$ 349,100,000
Service cost			7,100,000	5,900,000	7,200,000
Interest cost			$ 17,300,000	$ 17,500,000	$ 15,600,000
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets			4.50%	6.00%	6.00%
Discount rate for obligations			4.10%	3.71%	4.58%
Estimated contribution to the defined benefit plans next year			$ 1,100,000
Discount rate			3.81%	4.51%	4.58%
Defined Benefit Plan, Fair Value of Plan Assets			$ 2,800,000	$ 3,300,000	$ 3,700,000
Service cost			200,000	200,000	200,000
Interest cost			$ 600,000	$ 800,000	$ 800,000
Postretirement [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets			4.50%	6.00%	6.00%
Discount rate for obligations			4.10%	3.71%	4.58%
Estimated contribution to the defined benefit plans next year			$ 1,100,000
Discount rate			3.81%	4.51%	4.58%
Defined Benefit Plan, Fair Value of Plan Assets			$ 2,800,000	$ 3,300,000	$ 3,700,000
Service cost			200,000	200,000	200,000
Interest cost			600,000	$ 800,000	$ 800,000
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated contribution to the defined benefit plans next year			400,000
SERP [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated contribution to the defined benefit plans next year			$ 400,000
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets, fixed income securities, minimum			18.00%
Target allocations for plan assets, fixed income securities, maximum			38.00%
Equity Securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets, fixed income securities, minimum			18.00%
Target allocations for plan assets, fixed income securities, maximum			38.00%
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets, fixed income securities, minimum			58.00%
Target allocations for plan assets, fixed income securities, maximum			86.00%
Fixed Income Securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets, fixed income securities, minimum			58.00%
Target allocations for plan assets, fixed income securities, maximum			86.00%
Scenario, Forecast [Member] | Defined Benefit Plan [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 400,000
Interest cost		$ 3,100,000
Scenario, Forecast [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets		6.50%
Discount rate for obligations		4.49%
Scenario, Forecast [Member] | Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets		6.50%
Discount rate for obligations		4.49%
Service cost		$ 400,000
Interest cost		$ 3,200,000
Scenario, Forecast [Member] | Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets		3.90%
Discount rate for obligations		4.10%
Scenario, Forecast [Member] | Postretirement [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets		3.90%
Discount rate for obligations		4.10%
Scenario, Forecast [Member] | SERP [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 0
Interest cost		$ 100,000
Increase in Expected Rate of Return [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in Expected rate of return on plan assets			1.00%
Change in Pension Expense			$ (3,500,000)
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%
Change in Pension Expense			$ (3,500,000)
Decrease in Expected Rate of Return [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in Expected rate of return on plan assets			1.00%
Change in Pension Expense			$ 3,500,000
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%
Change in Pension Expense			$ 3,500,000
Expected Increase in Discount Rate [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in Pension Expense			$ (200,000)
Change in Discount Rate			0.25%
Expected Increase in Discount Rate [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in Pension Expense			$ (200,000)
Change in Discount Rate			0.25%
Expected Decrease in Discount Rate [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in Pension Expense			$ 300,000
Change in Discount Rate			0.25%
Expected Decrease in Discount Rate [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Change in Pension Expense			$ 300,000
Change in Discount Rate			0.25%
Change in Assumed Health Care Cost Trend Rate [Member]
Defined Benefit Plan Disclosure [Line Items]
Effect on postemployment benefit costs of change in assumed health care cost trend rate (less than)			$ 1,000,000
Change in Assumed Health Care Cost Trend Rate [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Effect on postemployment benefit costs of change in assumed health care cost trend rate (less than)			$ 1,000,000
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			$ 2,100
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			$ 2,100
Subsequent Event [Member] | Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension Contributions	$ 5,000,000
Subsequent Event [Member] | Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension Contributions	$ 5,000,000