Goodwill And Other Intangible Assets (Change In Goodwill) (Details) - USD ($) $ in Millions		3 Months Ended				12 Months Ended
		Dec. 31, 2015	Mar. 31, 2015	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Sep. 30, 2015	Sep. 30, 2014
Goodwill [Line Items]
Goodwill impairment	[1]					$ 0.0	$ (317.0)	$ (135.8)
THE DAYTON POWER AND LIGHT COMPANY [Member]
Goodwill [Line Items]
Goodwill		$ 2,440.5					2,440.5	2,440.5
Accumulated impairment losses		(2,440.5)					(2,440.5)	(2,123.5)
Goodwill, net balance		0.0					0.0	$ 317.0	$ 317.0
Goodwill impairment		$ (317.0)	$ (317.0)				$ (317.0)
DPLER [Member]
Goodwill [Line Items]
Goodwill, net balance					$ 135.8					$ 135.8
Goodwill impairment				$ (135.8)	$ (135.8)

[1] Goodwill impairment of $135.8 million in 2014 has been reclassified to Discontinued operations in the Consolidated Statement of Operations.