Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Entity Information [Line Items]
Effective income tax rates	14.10%	8.00%
Effective Income Tax Rate Reconciliation, at Combined Federal and State Statutory Income Tax Rate, Percent	21.60%
Estimated annual effective income tax rate	14.10%	19.20%
Non-cash capital contribution	$ 1.5	$ 44.6
THE DAYTON POWER AND LIGHT COMPANY [Member]
Entity Information [Line Items]
Effective income tax rates	17.40%	18.70%
Effective Income Tax Rate Reconciliation, at Combined Federal and State Statutory Income Tax Rate, Percent	21.60%
Estimated annual effective income tax rate	17.30%	19.80%