Property, Plant and Equipment (Changes in the Liability for Transmission and Distribution Asset Removal Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Changes in Liability for Transmission and Distribution Asset Removal Costs [Roll Forward]
Balance at January 1	$ 119.3	$ 115.0
Additions	24.3	19.6
Settlements	(21.8)	(15.3)
Balance at December 31	121.8	119.3
THE DAYTON POWER AND LIGHT COMPANY [Member]
Changes in Liability for Transmission and Distribution Asset Removal Costs [Roll Forward]
Balance at January 1	119.3	115.0
Additions	24.3	19.6
Settlements	(21.8)	(15.3)
Balance at December 31	$ 121.8	$ 119.3