Property, Plant and Equipment (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) generating_facility	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Number of generating facilities | generating_facility	5
Fixed asset impairment	$ 0.0	$ 11.5	$ 26.2
Estimated costs of removal	$ 121.8	119.3	115.0
THE DAYTON POWER AND LIGHT COMPANY [Member]
Jointly Owned Utility Plant Interests [Line Items]
Number of generating facilities | generating_facility	5
Fixed asset impairment	$ 0.0	0.0	86.0
Estimated costs of removal	$ 121.8	119.3	$ 115.0
East Bend Station [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Jointly Owned Utility Plant Interests [Line Items]
Fixed asset impairment		$ 86.0