Shareholder's Equity (Details) - USD ($) $ / shares in Units, $ 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	Dec. 31, 2018
Class of Stock [Line Items]
Non-cash capital contribution	$ (1.5)	$ 1.5	$ (17.9)	$ 44.6	$ 0.0	$ 26.7
Common Stock, Shares Authorized	1,500		1,500		1,500	1,500	1,500
Common stock, shares outstanding	1				1		1
THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Common Stock, Shares Authorized	50,000,000		50,000,000		50,000,000	50,000,000	50,000,000
Par value common shares (in USD per share)	$ 0.01		$ 0.01		$ 0.01	$ 0.01	$ 0.01
Common stock, shares outstanding	41,172,173				41,172,173		41,172,173
Proceeds from Contributions from Parent	$ (70.0)			$ 80.0	$ 0.0	$ 80.0
Payments of Ordinary Dividends, Common Stock					$ 70.0	$ 23.8