Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Depreciation / property basis	$ (539.8)	$ (548.2)
Income taxes recoverable	(12.0)	(14.8)
Regulatory assets	(10.6)	(18.0)
Investment tax credit	0.7	1.5
Compensation and employee benefits	3.1	3.2
Intangibles	(8.4)	(7.0)
Long-term debt	(1.1)	(1.5)
Other	(0.6)	(2.5)
Net non-current liabilities	(568.7)	(587.3)
Other	0.0	1.1
Net current assets	$ 0.0	1.1
Estimated Annual Effective Income Tax Rate, Continuing Operations	35.00%
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	$ 0.2	0.4	$ 0.0
Deferred tax assets related to state and local tax net operating loss carryforwards, net of related valuation allowances	26.0	27.1
Deferred tax assets related to state and local net operating loss carryforwards, valuation allowances	17.2	18.9
THE DAYTON POWER AND LIGHT COMPANY [Member]
Income Taxes [Line Items]
Depreciation / property basis	(608.8)	(618.8)
Income taxes recoverable	(12.0)	(14.8)
Regulatory assets	(11.5)	(18.0)
Investment tax credit	7.0	8.6
Compensation and employee benefits	3.6	5.2
Other	(9.5)	(12.2)
Net non-current liabilities	(631.2)	(650.0)
Other	0.0	0.5
Net current assets	$ 0.0	0.5
Estimated Annual Effective Income Tax Rate, Continuing Operations	35.00%
Additional tax increase / decrease	$ (0.4)	$ 0.7	$ (1.1)