Shareholder's Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Class of Stock [Line Items]
Non-cash capital contribution	$ 1.5	$ 44.6
Common Stock, Shares Authorized	1,500	1,500	1,500
Common stock, shares outstanding	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
Par value common shares (in USD per share)	$ 0.01	$ 0.01	$ 0.01
Common stock, shares outstanding	41,172,173		41,172,173
Proceeds from Contributions from Parent	$ 0.0	$ 80.0
Payments of Ordinary Dividends, Common Stock	$ 0.0	$ 23.8