Derivative Instruments and Hedging Activities (Fair Value and Balance Sheet Location (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Derivative Liability, Fair Value	$ 27.5
Derivative Liability, Fair Value, Amount Offset Against Collateral	17.9
THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Liability, Fair Value	27.5
Derivative Liability, Fair Value, Amount Offset Against Collateral	17.9
Total Assets [Member]
Derivative Asset, Fair Value	30.7	$ 14.9
Derivative, Collateral, Obligation to Return Securities	(17.9)	(6.6)
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	12.8	8.3
Total Assets [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Asset, Fair Value	30.8	15.1
Derivative, Collateral, Obligation to Return Securities	(17.9)	(6.6)
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	12.9	8.5
Total Liabilities [Member]
Derivative Liability, Fair Value	27.5	12.2
Derivative, Collateral, Right to Reclaim Securities	(17.9)	(6.6)
Derivative, Collateral, Right to Reclaim Cash	(8.0)	(4.9)
Derivative Liability, Fair Value, Amount Offset Against Collateral	1.6	0.7
Total Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Liability, Fair Value	27.5	12.3
Derivative, Collateral, Right to Reclaim Securities	(17.9)	(6.6)
Derivative, Collateral, Right to Reclaim Cash	(8.0)	(4.9)
Derivative Liability, Fair Value, Amount Offset Against Collateral	1.6	0.8
Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value	16.2	5.6
Derivative, Collateral, Obligation to Return Securities	(7.1)	(2.0)
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	9.1	3.6
Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Asset, Fair Value	16.2	5.6
Derivative, Collateral, Obligation to Return Securities	(7.1)	(2.0)
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	9.1	3.6
Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative Liability, Fair Value	7.1	2.1
Derivative, Collateral, Right to Reclaim Securities	(7.1)	(2.0)
Derivative, Collateral, Right to Reclaim Cash	0.0	0.0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0.0	0.1
Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Liability, Fair Value	7.1	2.1
Derivative, Collateral, Right to Reclaim Securities	(7.1)	(2.0)
Derivative, Collateral, Right to Reclaim Cash	0.0	0.0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0.0	0.1
Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member]
Derivative Asset, Fair Value	3.0	0.3
Derivative, Collateral, Obligation to Return Securities	(2.4)	(0.3)
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	0.6	0.0
Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Asset, Fair Value	3.0	0.3
Derivative, Collateral, Obligation to Return Securities	(2.4)	(0.3)
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	0.6	0.0
Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member]
Derivative Liability, Fair Value	2.7	0.6
Derivative, Collateral, Right to Reclaim Securities	(2.4)	(0.3)
Derivative, Collateral, Right to Reclaim Cash	0.0	(0.3)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0.3	0.0
Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Liability, Fair Value	2.7	0.6
Derivative, Collateral, Right to Reclaim Securities	(2.4)	(0.3)
Derivative, Collateral, Right to Reclaim Cash	0.0	(0.3)
Derivative Liability, Fair Value, Amount Offset Against Collateral	0.3	0.0
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value	7.3	5.5
Derivative, Collateral, Obligation to Return Securities	(5.5)	(3.4)
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	1.8	2.1
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Asset, Fair Value	7.4	5.6
Derivative, Collateral, Obligation to Return Securities	(5.5)	(3.4)
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	1.9	2.2
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative Liability, Fair Value	14.5	7.5
Derivative, Collateral, Right to Reclaim Securities	(5.5)	(3.4)
Derivative, Collateral, Right to Reclaim Cash	(8.0)	(4.1)
Derivative Liability, Fair Value, Amount Offset Against Collateral	1.0	0.0
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Liability, Fair Value	14.5	7.5
Derivative, Collateral, Right to Reclaim Securities	(5.5)	(3.4)
Derivative, Collateral, Right to Reclaim Cash	(8.0)	(4.1)
Derivative Liability, Fair Value, Amount Offset Against Collateral	1.0	0.0
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member]
Derivative Asset, Fair Value	4.0	3.5
Derivative, Collateral, Obligation to Return Securities	(2.7)	(0.9)
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	1.3	2.6
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Asset [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Asset, Fair Value	4.0	3.6
Derivative, Collateral, Obligation to Return Securities	(2.7)	(0.9)
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	1.3	2.7
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member]
Derivative Liability, Fair Value	2.7	0.9
Derivative, Collateral, Right to Reclaim Securities	(2.7)	(0.9)
Derivative, Collateral, Right to Reclaim Cash	0.0	0.0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0.0	0.0
Not Designated as Hedging Instrument [Member] | Forward Contract Power [Member] | Long-term Derivative Positions [Member] | Other Deferred Credit [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Liability, Fair Value	2.7	1.0
Derivative, Collateral, Right to Reclaim Securities	(2.7)	(0.9)
Derivative, Collateral, Right to Reclaim Cash	0.0	0.0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0.0	0.1
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member]
Derivative Asset, Fair Value	0.2
Derivative, Collateral, Obligation to Return Securities	(0.2)
Derivative, Collateral, Obligation to Return Cash	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	0.0
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Asset, Fair Value	0.2	0.0
Derivative, Collateral, Obligation to Return Securities	(0.2)	0.0
Derivative, Collateral, Obligation to Return Cash	0.0	0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral	0.0	0.0
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative Liability, Fair Value	0.5	0.6
Derivative, Collateral, Right to Reclaim Securities	(0.2)	0.0
Derivative, Collateral, Right to Reclaim Cash	0.0	0.0
Derivative Liability, Fair Value, Amount Offset Against Collateral	0.3	0.6
Not Designated as Hedging Instrument [Member] | Commodity Contract - FTR [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Liability, Fair Value	0.5	0.6
Derivative, Collateral, Right to Reclaim Securities	(0.2)	0.0
Derivative, Collateral, Right to Reclaim Cash	0.0	0.0
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ 0.3	0.6
Not Designated as Hedging Instrument [Member] | Commodity Contract - Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Prepayments and Current Assets [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Asset, Fair Value		0.0
Derivative, Collateral, Obligation to Return Securities		0.0
Derivative, Collateral, Obligation to Return Cash		0.0
Derivative Asset, Fair Value, Amount Offset Against Collateral		0.0
Not Designated as Hedging Instrument [Member] | Commodity Contract - Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative Liability, Fair Value		0.4
Derivative, Collateral, Right to Reclaim Securities		0.0
Derivative, Collateral, Right to Reclaim Cash		(0.4)
Derivative Liability, Fair Value, Amount Offset Against Collateral		0.0
Not Designated as Hedging Instrument [Member] | Commodity Contract - Heating Oil [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Liability, Fair Value		0.4
Derivative, Collateral, Right to Reclaim Securities		0.0
Derivative, Collateral, Right to Reclaim Cash		(0.4)
Derivative Liability, Fair Value, Amount Offset Against Collateral		0.0
Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member]
Derivative Liability, Fair Value		0.1
Derivative, Collateral, Right to Reclaim Securities		0.0
Derivative, Collateral, Right to Reclaim Cash		(0.1)
Derivative Liability, Fair Value, Amount Offset Against Collateral		0.0
Not Designated as Hedging Instrument [Member] | Natural Gas [Member] | Short-term Derivative Positions [Member] | Other Current Liabilities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Derivative Liability, Fair Value		0.1
Derivative, Collateral, Right to Reclaim Securities		0.0
Derivative, Collateral, Right to Reclaim Cash		(0.1)
Derivative Liability, Fair Value, Amount Offset Against Collateral		$ 0.0