Benefit Plans (Other Changes in Plan Assets and Benefit Obligation Recognized in Accumulated Other Comprehensive Income, Regulatory Assets And Regulatory Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Postretirement [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	$ (1.1)	$ 0.4	$ (2.0)
Reversal of amortization item, Net actuarial (gain) / loss	0.6	0.6	0.5
Reversal of amortization item, Prior service cost / (credit)	(0.1)	0.0	0.0
Total recognized in Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	(0.6)	1.0	(1.5)
Total recognized in net periodic benefit cost and Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	(0.4)	1.2	(1.1)
Postretirement [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss		(1.1)	0.4	$ (1.9)
Reversal of amortization item, Net actuarial (gain) / loss		0.6	0.8	0.7
Reversal of amortization item, Prior service cost / (credit)		(0.1)	(0.1)	(0.1)
Total recognized in Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities		(0.6)	1.1	(1.3)
Total recognized in net periodic benefit cost and Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities		(0.4)	1.2	$ (1.1)
Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	(3.0)	43.8	(12.0)
Prior service cost / (credit)	0.0	6.8	0.0
Reversal of amortization item, Net actuarial (gain) / loss	(5.8)	(3.4)	(4.9)
Reversal of amortization item, Prior service cost / (credit)	(2.0)	(1.5)	(1.5)
Total recognized in Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	(10.8)	45.7	(18.4)
Total recognized in net periodic benefit cost and Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	(1.2)	51.1	(12.5)
Pension [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) / loss	(3.0)	43.8	(11.7)
Prior service cost / (credit)	0.0	6.8	0.0
Reversal of amortization item, Net actuarial (gain) / loss	(9.8)	(6.4)	(9.3)
Reversal of amortization item, Prior service cost / (credit)	(3.3)	(2.8)	(2.8)
Total recognized in Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	(16.1)	41.4	(23.8)
Total recognized in net periodic benefit cost and Accumulated other comprehensive income, Regulatory assets and Regulatory liabilities	$ (1.2)	$ 51.1	$ (12.5)