Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 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							(10.10%)	16.80%
Effective Income Tax Rate Reconciliation, Including Discontinued Operations, Percent	(35.60%)			16.30%			(9.80%)	15.20%
Non-cash capital contribution	$ 2.7	$ (1.5)	$ 1.5	$ 3.5	$ (17.9)	$ 44.6	$ 2.7	$ 30.2
THE DAYTON POWER AND LIGHT COMPANY [Member]
Entity Information [Line Items]
Effective income tax rates				16.80%				16.20%
Effective Income Tax Rate Reconciliation, at Combined Federal and State Statutory Income Tax Rate, Percent							21.60%
Estimated annual effective income tax rate							4.50%	17.10%
Effective Income Tax Rate Reconciliation, Including Discontinued Operations, Percent	(19.10%)						4.70%