Property, Plant and Equipment with Corresponding Depreciation Rates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Public Utility, Property, Plant and Equipment [Line Items]
Total property, plant and equipment in service	$ 1,985.6	$ 2,850.7
Total property, plant and equipment in service, Composite Rate	6.10%	4.40%	5.30%
Regulated Operation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	$ 247.3	$ 239.4
Distribution	1,141.1	1,085.7
General	13.7	13.9
Non-depreciable	63.5	62.5
Total property, plant and equipment in service	$ 1,465.6	$ 1,401.5
Transmission, Composite Rate	3.90%	3.90%
Distribution, Composite Rate	4.70%	5.00%
General, Composite Rate	7.40%	7.20%
Unregulated Operation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Non-depreciable	$ 19.8	$ 19.8
Total property, plant and equipment in service	520.0	1,449.2
Production / Generation	$ 483.2	$ 1,413.1
Production/Generation, Composite Rate	11.70%	4.20%
Other	$ 17.0	$ 16.3
Other, Composite Rate	8.00%	12.10%
THE DAYTON POWER AND LIGHT COMPANY [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Total property, plant and equipment in service	$ 2,398.6	$ 5,172.3
Total property, plant and equipment in service, Composite Rate	4.60%	2.50%	2.80%
THE DAYTON POWER AND LIGHT COMPANY [Member] | Regulated Operation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Transmission	$ 421.1	$ 413.7
Distribution	1,693.5	1,639.7
General	31.6	31.6
Non-depreciable	63.5	62.5
Total property, plant and equipment in service	$ 2,209.7	$ 2,147.5
Transmission, Composite Rate	2.30%	2.30%
Distribution, Composite Rate	3.20%	3.30%
General, Composite Rate	3.20%	3.20%
THE DAYTON POWER AND LIGHT COMPANY [Member] | Unregulated Operation [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Non-depreciable	$ 188.9	$ 3,024.8
Production / Generation	$ 173.9	$ 3,009.8
Production/Generation, Composite Rate	26.20%	2.10%
Other	$ 15.0	$ 15.0