Property, Plant and Equipment (Changes in the Liability for Generation of AROs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1	$ 26.9	$ 24.4
Additions	40.3	3.6
Accretion expense	1.9	0.9
Settlements	(3.2)	(2.0)
Balance at December 31	65.9	26.9
THE DAYTON POWER AND LIGHT COMPANY [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at January 1	22.9	19.9
Additions	40.3	3.6
Accretion expense	2.1	1.1
Settlements	(3.2)	(1.7)
Balance at December 31	$ 62.1	$ 22.9