Equity (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Oct. 01, 2017 USD ($)
Class of Stock [Line Items]
Maximum leverage ratio to allow distribution to shareholder	0.67
Minimum coverage ratio to allow distribution to shareholder	2.50
Retained earnings / (deficit)	$ (2,739.0)	$ (2,844.4)
Common stock, shares authorized | shares	1,500	1,500
Common stock, shares outstanding | shares	1	1
Leverage Ratio	1.32
Accounts Payable, Related Parties, Current	$ 11.0	$ 4.8
Non-cash capital contribution		40.0	$ 97.1
THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Retained earnings / (deficit)	$ (107.1)	$ (231.6)
Common stock, shares authorized | shares	50,000,000	50,000,000
Common stock, shares outstanding | shares	41,172,173	41,172,173
Accounts Payable, Related Parties, Current	$ 11.0	$ 4.8
Proceeds from Contributions from Parent	0.0	80.0	70.0
Dividends, Common Stock, Cash	95.0	(43.8)	39.0	$ 70.0
Payments of Ordinary Dividends, Common Stock	95.0	43.8	39.0
Other Paid-In Capital [Member]
Class of Stock [Line Items]
Non-cash capital contribution	0.0	40.0	97.1
Other Paid-In Capital [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Proceeds from Contributions from Parent		(80.0)	(70.0)
Dividends, Common Stock, Cash	95.0	43.8	39.0
Generation [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Class of Stock [Line Items]
Disposal Group, Including Discontinued Operation, Net Assets	$ 0.0	$ 10.0	$ 86.2		$ 86.2