Fixed-asset Impairment (Narrative) (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2014 MW	Dec. 31, 2013 USD ($) MW	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Public Utility, Property, Plant and Equipment [Line Items]
Fixed asset impairment			$ 0.0	$ 11.5	$ 26.2
THE DAYTON POWER AND LIGHT COMPANY [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Fixed asset impairment			0.0	0.0	86.0
East Bend Station [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Fixed asset impairment			0.0	11.5	0.0
Fair Value				2.7
East Bend Station [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Fixed asset impairment			0.0	0.0	76.0
Production Plan Capacity | MW	186	186
Conesville [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Fixed asset impairment			0.0	0.0	26.2
Production Plan Capacity | MW		129
Fair Value		$ 0.0			0.0
Conesville [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Fixed asset impairment			$ 0.0	$ 0.0	10.0
Production Plan Capacity | MW		129
Fair Value		$ 0.0			$ 0.0