Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Entity Information [Line Items]
Effective Income Tax Rate Reconciliation, at Combined Federal and State Statutory Income Tax Rate, Percent	22.30%
Estimated annual effective income tax rate	(14.90%)	14.30%
Effective Income Tax Rate Reconciliation, Including Discontinued Operations, Percent	(11.80%)	14.30%
Non-cash capital contribution	$ 0.0	$ 1.5
THE DAYTON POWER AND LIGHT COMPANY [Member]
Entity Information [Line Items]
Effective income tax rates		17.40%
Effective Income Tax Rate Reconciliation, at Combined Federal and State Statutory Income Tax Rate, Percent	22.30%
Estimated annual effective income tax rate	9.10%	17.30%
Effective Income Tax Rate Reconciliation, Including Discontinued Operations, Percent	9.30%	9.30%