Income Taxes (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Income Taxes [Line Items]
Unrecognized tax benefits due to uncertainty in timing of deductibility	$ 0.9
THE DAYTON POWER AND LIGHT COMPANY [Member]
Income Taxes [Line Items]
Unrecognized tax benefits due to uncertainty in timing of deductibility	$ 0.9