Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Entity Information [Line Items]
Effective Income Tax Rate Reconciliation, at Combined Federal and State Statutory Income Tax Rate, Percent					21.60%
Estimated annual effective income tax rate					12.30%	16.50%
Effective Income Tax Rate Reconciliation, Including Discontinued Operations, Percent	16.60%		(12.90%)		12.80%	13.90%
Non-cash capital contribution	$ (1.5)	$ 1.5	$ (17.9)	$ 44.6	$ 0.0	$ 26.7
THE DAYTON POWER AND LIGHT COMPANY [Member]
Entity Information [Line Items]
Effective income tax rates	17.20%		12.30%		17.30%	15.70%
Effective Income Tax Rate Reconciliation, at Combined Federal and State Statutory Income Tax Rate, Percent					21.60%
Estimated annual effective income tax rate					17.10%	17.20%