Equity (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Retained earnings / (deficit)	$ (2,717.9)	$ (2,740.0)
Common stock, shares authorized	1,500	1,500
Common stock, shares outstanding	1	1
Accounts Payable, Related Parties, Current	$ 24.7	$ 14.8
Non-cash capital contribution		98.0
Cash Contribution from Parent Company	150.0	150.0
Payment against tax receivable balance from Parent	17.5	52.0
THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Retained earnings / (deficit)	$ (8.9)	$ (56.0)
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares outstanding	41,172,173	41,172,173
Accounts Payable, Related Parties, Current	$ 24.7	$ 14.8
Dividends, Common Stock, Cash	42.0	(52.7)	$ 95.0
Payments of Ordinary Dividends, Common Stock	52.0		95.0
Other Paid-In Capital [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Dividends, Common Stock, Cash	42.0	52.7	95.0
Payments of Ordinary Dividends, Common Stock	52.0	42.7
Dividends, Common Stock	$ 42.0	$ 42.7	$ 95.0