Schedule II Valuation And Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Provision for Uncollectible Accounts [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 2.8	$ 0.4	$ 0.9
Additions	(0.4)	3.0	3.0
Deductions	2.1	0.6	3.5
Balance at End of Period	0.3	2.8	0.4
Provision for Uncollectible Accounts [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	2.8	0.4	0.9
Additions	(0.4)	3.0	3.0
Deductions	2.1	0.6	3.5
Balance at End of Period	0.3	2.8	0.4
Valuation Allowance For Deferred Tax Assets [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	39.0	29.0	29.9
Additions	1.5	11.0	2.2
Deductions	3.4	1.0	3.1
Balance at End of Period	$ 37.1	$ 39.0	$ 29.0