Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Federal - Current	$ (5.5)	$ (45.1)	$ (22.0)
State and Local - Current	0.0	(0.1)	0.6
Total Current	(5.5)	(45.2)	(21.4)
Federal - Deferred	4.4	38.7	14.1
State and Local - Deferred	0.4	1.1	1.1
Total Deferred	4.8	39.8	15.2
Income Tax Expense (Benefit), Continuing Operations, Discontinued Operations	(0.7)	(5.4)	(6.2)
THE DAYTON POWER AND LIGHT COMPANY [Member]
Income Taxes [Line Items]
Federal - Current	1.1	3.5	8.6
State and Local - Current	0.1	0.1	0.6
Total Current	1.2	3.6	9.2
Federal - Deferred	4.1	2.4	(10.9)
State and Local - Deferred	0.4	1.0	1.1
Total Deferred	4.5	3.4	(9.8)
Income Tax Expense (Benefit), Continuing Operations, Discontinued Operations	$ 5.7	$ 7.0	$ (0.6)