Benefit Plans (Estimated Amounts that will be Amortized from Accumulated Other Comprehensive Income, Regulatory Assets And Regulatory Liabilities) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	$ 4.3
Prior service cost	1.9
Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	7.2
Prior service cost	3.1
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	(0.6)
Prior service cost	0.1
Postretirement [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	(0.8)
Prior service cost	$ 0.1