Property, Plant and Equipment with Corresponding Depreciation Rates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Public Utility, Property, Plant and Equipment [Line Items]
Total property, plant and equipment in service	$ 2,909.0	$ 2,754.1
Total property, plant and equipment in service, Composite Rate	4.60%	5.30%	5.80%
Regulated Operation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	$ 239.4	$ 227.5
Distribution	1,085.7	1,011.7
General	65.9	62.5
Non-depreciable	62.5	61.6
Total property, plant and equipment in service	$ 1,453.5	$ 1,363.3
Transmission, Composite Rate	3.90%	4.10%
Distribution, Composite Rate	5.00%	5.40%
General, Composite Rate	12.40%	12.40%
Unregulated Operation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Non-depreciable	$ 19.8	$ 19.8
Total property, plant and equipment in service	1,455.5	1,390.8
Production / Generation	$ 1,418.7	$ 1,354.9
Production/Generation, Composite Rate	4.20%	5.40%
Other	$ 17.0	$ 16.1
Other, Composite Rate	8.10%	5.50%
THE DAYTON POWER AND LIGHT COMPANY [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total property, plant and equipment in service	$ 5,244.7	$ 5,120.7
Total property, plant and equipment in service, Composite Rate	2.60%	2.80%	4.40%
THE DAYTON POWER AND LIGHT COMPANY [Member] | Regulated Operation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	$ 413.7	$ 402.4
Distribution	1,639.7	1,568.0
General	96.9	116.1
Non-depreciable	62.5	61.6
Total property, plant and equipment in service	$ 2,212.8	$ 2,148.1
Transmission, Composite Rate	2.30%	2.30%
Distribution, Composite Rate	3.30%	3.50%
General, Composite Rate	8.40%	6.70%
THE DAYTON POWER AND LIGHT COMPANY [Member] | Unregulated Operation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Non-depreciable	$ 3,031.9	$ 2,972.6
Production / Generation	$ 3,016.8	$ 2,957.7
Production/Generation, Composite Rate	2.10%	2.40%
Other	$ 15.1	$ 14.9