Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Federal income tax	$ (81.0)	$ 25.4	$ (71.7)
State income taxes, net of federal effect	(0.1)	0.8	1.1
Depreciation of AFUDC - Equity	(3.5)	(3.4)	(3.2)
Investment tax credit amortized	(0.5)	(0.5)	(0.5)
Section 199 - domestic production deduction	(4.1)	(1.1)	(4.1)
Non-deductible goodwill impairment	111.0	0.0	107.2
Accrual (settlement) for open tax years	0.0	(6.6)	(8.8)
Other, net	(1.8)	0.8	(0.2)
Total tax expense	20.0	15.4	19.8
Federal - Current	30.1	(5.2)	(2.5)
State and Local - Current	0.8	0.4	0.0
Total Current	30.9	(4.8)	(2.5)
Federal - Deferred	(9.9)	19.6	20.6
State and Local - Deferred	(1.0)	0.6	1.7
Total Deferred	(10.9)	20.2	22.3
THE DAYTON POWER AND LIGHT COMPANY [Member]
Income Taxes [Line Items]
Federal income tax	49.3	53.8	35.5
State income taxes, net of federal effect	0.4	1.2	0.3
Depreciation of AFUDC - Equity	(2.8)	(2.7)	(2.5)
Investment tax credit amortized	(2.4)	(2.5)	(2.5)
Section 199 - domestic production deduction	(6.1)	(4.6)	(4.1)
Accrual (settlement) for open tax years	0.0	(6.6)	(8.8)
Other, net	(3.3)	1.1	0.7
Total tax expense	35.1	39.7	18.6
Federal - Current	55.8	34.1	38.6
State and Local - Current	0.8	0.5	(0.1)
Total Current	56.6	34.6	38.5
Federal - Deferred	(21.0)	4.1	(20.4)
State and Local - Deferred	(0.5)	1.0	0.5
Total Deferred	$ (21.5)	$ 5.1	$ (19.9)