Summary of Signficant Accounting Policies (Accounting for Taxes Collected from Customers and Remitted to Governmental Authorities) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Significant Accounting Policies [Line Items]
Excise taxes collected	$ 13.0	$ 12.5	$ 38.5	$ 38.5
THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Excise taxes collected	$ 13.0	$ 12.5	$ 38.5	$ 38.5