Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 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				71.10%	12.30%
Effective Income Tax Rate Reconciliation, Including Discontinued Operations, Percent	50.00%	16.60%		37.20%	12.80%
Non-cash capital contribution	$ 98.0	$ (1.5)	$ 1.5
THE DAYTON POWER AND LIGHT COMPANY [Member]
Entity Information [Line Items]
Effective income tax rates		17.20%			17.30%
Effective Income Tax Rate Reconciliation, at Combined Federal and State Statutory Income Tax Rate, Percent				22.30%
Effective Income Tax Rate Reconciliation, Including Discontinued Operations, Percent	(14.80%)			(3.90%)