Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Entity Information [Line Items]
Effective income tax rates	21.70%	29.70%	26.20%	32.70%
Estimated annual effective income tax rate			16.50%	30.90%
Federal Income Tax Rate for Corporations			21.00%	35.00%
Non-cash capital contribution			$ 26.7	$ 0.0
THE DAYTON POWER AND LIGHT COMPANY [Member]
Entity Information [Line Items]
Effective income tax rates	12.30%	25.20%	15.70%	29.40%
Estimated annual effective income tax rate			17.20%	30.40%
Federal Income Tax Rate for Corporations			21.00%	35.00%