Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Entity Information [Line Items]
Effective income tax rates	94.30%	39.20%	31.20%	39.50%
Estimated annual effective income tax rate			30.90%	38.80%
THE DAYTON POWER AND LIGHT COMPANY [Member]
Entity Information [Line Items]
Effective income tax rates	38.80%	36.40%	31.30%	36.90%
Estimated annual effective income tax rate			30.40%	36.70%
Income Taxes Paid, Net			$ 26.2	$ 0.1