Fair Value (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Unrealized Gain (Loss) on Investments	$ 0.8	$ 0.2	$ (0.3)	$ 0.7
THE DAYTON POWER AND LIGHT COMPANY [Member]
Unrealized Gain (Loss) on Investments	$ 0.8	$ 0.2	$ (0.3)	$ 0.7

Amount of unrealized gain (loss) on investment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration