Derivative Instruments and Hedging Activities (Classification within the Condensed Consolidated Statements of Results of Operations or Balance Sheets of the Gains and Losses) (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Change in unrealized gain / (loss)	$ (1.6)	$ (1.8)
Realized gain / (loss)	(0.4)	(2.6)
Derivative, Gain (Loss) on Derivative, Net	(2.0)	(4.4)
Commodity Contract - Heating Oil [Member]
Change in unrealized gain / (loss)	0.0	0.1
Realized gain / (loss)	0.0	(0.1)
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Commodity Contract - FTR [Member]
Change in unrealized gain / (loss)	0.1	0.9
Realized gain / (loss)	0.2	(0.1)
Derivative, Gain (Loss) on Derivative, Net	0.3	0.8
Forward Contract Power [Member]
Change in unrealized gain / (loss)	(1.5)	(2.9)
Realized gain / (loss)	(0.4)	(2.3)
Derivative, Gain (Loss) on Derivative, Net	(1.9)	(5.2)
Natural Gas [Member]
Change in unrealized gain / (loss)	(0.2)	0.1
Realized gain / (loss)	(0.2)	(0.1)
Derivative, Gain (Loss) on Derivative, Net	(0.4)	0.0
THE DAYTON POWER AND LIGHT COMPANY [Member]
Change in unrealized gain / (loss)	(2.0)	(1.8)
Realized gain / (loss)	(0.3)	(2.6)
Derivative, Gain (Loss) on Derivative, Net	(2.3)	(4.4)
THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Change in unrealized gain / (loss)	0.0	0.1
Realized gain / (loss)	0.0	(0.1)
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Change in unrealized gain / (loss)	0.1	0.9
Realized gain / (loss)	0.2	(0.1)
Derivative, Gain (Loss) on Derivative, Net	0.3	0.8
THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Change in unrealized gain / (loss)	(1.9)	(2.9)
Realized gain / (loss)	(0.3)	(2.3)
Derivative, Gain (Loss) on Derivative, Net	(2.2)	(5.2)
THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Change in unrealized gain / (loss)	(0.2)	0.1
Realized gain / (loss)	(0.2)	(0.1)
Derivative, Gain (Loss) on Derivative, Net	(0.4)	0.0
Revenue [Member]
Derivative, Gain (Loss) on Derivative, Net	(1.1)	(0.3)
Revenue [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Revenue [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Revenue [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(1.1)	(0.3)
Revenue [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative, Gain (Loss) on Derivative, Net	(1.4)	(0.3)
Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(1.4)	(0.3)
Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Purchased Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.9)	(4.1)
Purchased Power [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Purchased Power [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	0.3	0.8
Purchased Power [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.8)	(4.9)
Purchased Power [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.4)	0.0
Purchased Power [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.9)	(4.1)
Purchased Power [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Purchased Power [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	0.3	0.8
Purchased Power [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(0.8)	(4.9)
Purchased Power [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net	$ (0.4)	$ 0.0