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	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Change in unrealized gain / (loss)	$ (5.6)	$ (3.0)	$ 0.9
Realized gain / (loss)	(10.4)	(3.1)	2.4
Derivative, Gain (Loss) on Derivative, Net	(16.0)	(6.1)	3.3
Commodity Contract - Heating Oil [Member]
Change in unrealized gain / (loss)	0.4	(0.6)	0.0
Realized gain / (loss)	(0.3)	(0.1)	0.1
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.7)	0.1
Commodity Contract - FTR [Member]
Change in unrealized gain / (loss)	0.3	(0.8)	0.3
Realized gain / (loss)	(0.2)	0.7	1.2
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.1)	1.5
Forward Contract Power [Member]
Change in unrealized gain / (loss)	(6.4)	(1.5)	0.6
Realized gain / (loss)	(9.8)	(3.6)	1.1
Derivative, Gain (Loss) on Derivative, Net	(16.2)	(5.1)	1.7
Natural Gas [Member]
Change in unrealized gain / (loss)	0.1	(0.1)
Realized gain / (loss)	(0.1)	(0.1)
Derivative, Gain (Loss) on Derivative, Net	0.0	(0.2)
THE DAYTON POWER AND LIGHT COMPANY [Member]
Change in unrealized gain / (loss)	(5.5)	(3.0)	(0.9)
Realized gain / (loss)	(10.5)	(2.5)	2.9
Derivative, Gain (Loss) on Derivative, Net	(16.0)	(5.5)	2.0
THE DAYTON POWER AND LIGHT COMPANY [Member] | NYMEX Coal Contract [Member]
Change in unrealized gain / (loss)			0.0
Realized gain / (loss)			0.0
Derivative, Gain (Loss) on Derivative, Net			0.0
THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Change in unrealized gain / (loss)	0.4	(0.6)	0.0
Realized gain / (loss)	(0.3)	(0.1)	0.1
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.7)	0.1
THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Change in unrealized gain / (loss)	0.3	(0.8)	0.3
Realized gain / (loss)	(0.2)	0.7	1.2
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.1)	1.5
THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Change in unrealized gain / (loss)	(6.3)	(1.5)	(1.2)
Realized gain / (loss)	(9.9)	(3.0)	1.6
Derivative, Gain (Loss) on Derivative, Net	(16.2)	(4.5)	0.4
THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Change in unrealized gain / (loss)	0.1	(0.1)
Realized gain / (loss)	(0.1)	(0.1)
Derivative, Gain (Loss) on Derivative, Net	0.0	(0.2)
Revenue [Member]
Derivative, Gain (Loss) on Derivative, Net	27.4		0.0
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	27.4		0.0
Revenue [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0
Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative, Gain (Loss) on Derivative, Net	27.4	0.7	0.2
Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | NYMEX Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	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	0.0
Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	27.4	0.7	0.2
Revenue [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Cost of Sales [Member]
Derivative, Gain (Loss) on Derivative, Net	(43.5)	(5.4)	3.2
Cost of Sales [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0	0.0
Cost of Sales [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.1)	1.5
Cost of Sales [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(43.6)	(5.1)	1.7
Cost of Sales [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	(0.2)
Cost of Sales [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative, Gain (Loss) on Derivative, Net	(43.5)	(5.5)	1.7
Cost of Sales [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | NYMEX Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
Cost of Sales [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0	0.0
Cost of Sales [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.1)	1.5
Cost of Sales [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	(43.6)	(5.2)	0.2
Cost of Sales [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	(0.2)
Fuel [Member]
Derivative, Gain (Loss) on Derivative, Net		(0.6)	0.1
Fuel [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net		(0.6)	0.1
Fuel [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net		0.0	0.0
Fuel [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net		0.0	0.0
Fuel [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net		0.0
Fuel [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	(0.6)	0.1
Fuel [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | NYMEX Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
Fuel [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	(0.6)	0.1
Fuel [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0	0.0
Fuel [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0	0.0
Fuel [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
O&M [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
O&M [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
O&M [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
O&M [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
O&M [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
O&M [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | NYMEX Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
O&M [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
O&M [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
O&M [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
Partners' Share of Gain [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
Partners' Share of Gain [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | NYMEX Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
Partners' Share of Gain [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
Partners' Share of Gain [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
Partners' Share of Gain [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
Regulatory Asset [Member]
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.1)
Regulatory Asset [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.1)
Regulatory Asset [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Regulatory Asset [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Regulatory Asset [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0
Regulatory Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.1)	0.0
Regulatory Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | NYMEX Coal Contract [Member]
Derivative, Gain (Loss) on Derivative, Net			0.0
Regulatory Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Derivative, Gain (Loss) on Derivative, Net	0.1	(0.1)	0.0
Regulatory Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0	0.0
Regulatory Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Derivative, Gain (Loss) on Derivative, Net	0.0	0.0	$ 0.0
Regulatory Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Derivative, Gain (Loss) on Derivative, Net	$ 0.0	$ 0.0