Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Taxes [Line Items]
Federal - Current	$ (20.0)	$ (7.6)	$ (5.5)
State and Local - Current	0.4	0.0	0.0
Total Current	(19.6)	(7.6)	(5.5)
Federal - Deferred	24.5	(2.1)	4.4
State and Local - Deferred	1.7	0.1	0.4
Total Deferred	26.2	(2.0)	4.8
Income Tax Expense (Benefit), Continuing Operations, Discontinued Operations	6.6	(9.6)	(0.7)
THE DAYTON POWER AND LIGHT COMPANY [Member]
Income Taxes [Line Items]
Federal - Current	4.1	(0.8)	1.1
State and Local - Current	0.4	0.0	0.1
Total Current	4.5	(0.8)	1.2
Federal - Deferred	7.3	(2.4)	4.1
State and Local - Deferred	1.7	0.1	0.4
Total Deferred	9.0	(2.3)	4.5
Income Tax Expense (Benefit), Continuing Operations, Discontinued Operations	$ 13.5	$ (3.1)	$ 5.7