Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Debt maturity date, earliest	2016
Debt maturity date, latest	2061
Unrealized gains and immaterial losses on Master Trust assets in AOCI	$ 0.7	$ 0.8
Unrealized gains and immaterial losses on Master Trust assets in AOCI, after tax	$ 0.5	0.5
Percent of inputs to the fair value of derivative instruments from quoted market prices	99.00%
Gross additions to our existing landfill and asbestos AROs	$ 39.0	2.5
Gross additions to our existing landfill and asbestos AROs, after tax	25.4	1.6
Increase (Decrease) in Asset Retirement Obligations	40.3
Increase (Decrease) in Asset Retirement Obligations after tax	(26.2)
Unrealized Losses in AOCI, Before Tax	0.1
Unrealized Losses in AOCI, Net of Tax	0.1
THE DAYTON POWER AND LIGHT COMPANY [Member]
Unrealized gains and immaterial losses on Master Trust assets in AOCI	0.8	1.1
Unrealized gains and immaterial losses on Master Trust assets in AOCI, after tax	$ 0.5	0.7
Percent of inputs to the fair value of derivative instruments from quoted market prices	99.00%
Gross additions to our existing landfill and asbestos AROs	$ 39.2	3.0
Gross additions to our existing landfill and asbestos AROs, after tax	25.5	$ 2.0
Increase (Decrease) in Asset Retirement Obligations	40.3
Increase (Decrease) in Asset Retirement Obligations after tax	(26.2)
Unrealized Losses in AOCI, Before Tax	0.1
Unrealized Losses in AOCI, Net of Tax	$ 0.1