Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2021	Jan. 01, 2020	Jan. 01, 2019
Income Taxes [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards	$ 37.1	$ 39.0
Deferred tax assets related to state and local tax net operating loss carryforwards, net of related valuation allowances	37.1	39.0
Unrecognized Tax Benefits	0.4	1.4	$ 3.5	$ 1.4	$ 3.5	$ 3.5
Decrease in Unrecognized Tax Benefits Due To Uncertainty In Timing of Deductibility	(1.0)	(2.1)	0.0
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]
Income Taxes [Line Items]
Unrecognized Tax Benefits	0.4	1.4	4.8	$ 1.4	$ 4.8	$ 4.8
Decrease in Unrecognized Tax Benefits Due To Uncertainty In Timing of Deductibility	(1.0)	$ (3.4)	$ 0.0
Forecast [Member]
Income Taxes [Line Items]
Unrecognized tax benefits anticipated to result in a decrease of unrecognized tax benefits with 12 months of the balance sheet date, minimum	$ 0.0