Fair Value Measurements (Fair Value of Assets and Liabilities Measured on a Nonrecurring Basis) (Details) - USD ($) $ in Millions			3 Months Ended		12 Months Ended
		Oct. 01, 2013	Dec. 31, 2015	Jun. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value			$ 2,561.7		$ 2,561.7	$ 2,512.6
Fixed asset impairment					0.0	11.5	$ 26.2
Goodwill			0.0		0.0	317.0	452.8
Goodwill impairment	[1]				317.0	135.8	306.3
THE DAYTON POWER AND LIGHT COMPANY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value			2,738.7		2,738.7	2,700.4
Fixed asset impairment					0.0	0.0	86.0
Goodwill		$ 317.0	0.0		0.0	317.0	317.0	$ 317.0			$ 623.3
Goodwill impairment		$ 306.3	317.0		317.0	0.0	306.3
THE DAYTON POWER AND LIGHT COMPANY [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill							317.0
DPLER [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill			$ 0.0		0.0	0.0	135.8		$ 135.8	$ 135.8
Goodwill impairment				$ 135.8	0.0	135.8
East Bend Station [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value							14.2
Long-lived assets held and used, fair value						2.7
Fixed asset impairment					0.0	11.5	0.0
East Bend Station [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets held and used, fair value						2.7
East Bend Station [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value											76.0
Fixed asset impairment					0.0	0.0	76.0
Conesville [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value											26.2
Long-lived assets held and used, fair value							0.0
Fixed asset impairment					0.0	0.0	26.2
Conesville [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value											$ 30.0
Long-lived assets held and used, fair value							0.0
Fixed asset impairment					$ 0.0	$ 0.0	10.0
Conesville [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets held and used, fair value							$ 20.0

[1] Goodwill impairment of $135.8 million in 2014 has been reclassified to Discontinued operations in the Consolidated Statement of Operations.