Benefit Plans (Estimated Amounts that will be Amortized from Accumulated Other Comprehensive Income, Regulatory Assets And Regulatory Liabilities) (Details) - Scenario, Forecast [Member] - Pension [Member] $ in Millions	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	$ 6.4
Prior service cost	0.9
THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	9.4
Prior service cost	$ 1.4