Shareholder's Equity (Details) - USD ($) $ / shares in Units, $ 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	Dec. 31, 2018
Class of Stock [Line Items]
Non-cash capital contribution	$ 2.7	$ (1.5)	$ 1.5	$ 3.5	$ (17.9)	$ 44.6	$ 2.7	$ 30.2
Common Stock, Shares Authorized	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							$ 90.0	$ 43.8