Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Level 1 [Member]
Total Master Trust Assets, Fair Value	$ 0.2	$ 8.9
Total Derivative Assets	0.0	0.0
Total Assets	0.2	8.9
Total Derivative Liabilities	0.0	0.5
Total Liabilities	0.0	0.5
Level 1 [Member] | Forward Contract Power [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities	0.0	0.0
Level 1 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.0
Total Derivative Liabilities	0.0	0.0
Level 1 [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities		0.4
Level 1 [Member] | Natural Gas [Member]
Total Derivative Liabilities		0.1
Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.2	8.9
Total Derivative Assets	0.0	0.0
Total Assets	0.2	8.9
Total Derivative Liabilities	0.0	0.5
Debt Instrument, Fair Value Disclosure	0.0	0.0
Total Liabilities	0.0	0.5
Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities	0.0	0.0
Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.0
Total Derivative Liabilities	0.0	0.0
Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities		0.4
Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Total Derivative Liabilities		0.1
Level 2 [Member]
Total Master Trust Assets, Fair Value	8.8	0.8
Total Derivative Assets	30.5	13.7
Total Assets	39.3	14.5
Total Derivative Liabilities	23.9	11.1
Total Liabilities	1,981.1	2,197.7
Level 2 [Member] | Forward Contract Power [Member]
Total Derivative Assets	30.5	13.7
Total Derivative Liabilities	23.9	11.1
Level 2 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.0
Total Derivative Liabilities	0.0	0.0
Level 2 [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities		0.0
Level 2 [Member] | Natural Gas [Member]
Total Derivative Liabilities		0.0
Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	8.8	0.8
Total Derivative Assets	30.6	13.9
Total Assets	39.4	14.7
Total Derivative Liabilities	23.9	11.2
Debt Instrument, Fair Value Disclosure	746.1	864.3
Total Liabilities	770.0	875.5
Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Total Derivative Assets	30.6	13.9
Total Derivative Liabilities	23.9	11.2
Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.0
Total Derivative Liabilities	0.0	0.0
Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities		0.0
Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Total Derivative Liabilities		0.0
Level 3 [Member]
Total Derivative Assets	0.2	1.2
Total Assets	0.2	1.2
Total Derivative Liabilities	3.6	0.6
Total Liabilities	21.7	18.8
Level 3 [Member] | Forward Contract Power [Member]
Total Derivative Assets	0.0	1.2
Total Derivative Liabilities	3.1	0.0
Level 3 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.2
Total Derivative Liabilities	0.5	0.6
Level 3 [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities		0.0
Level 3 [Member] | Natural Gas [Member]
Total Derivative Liabilities		0.0
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Derivative Assets	0.2	1.2
Total Assets	0.2	1.2
Total Derivative Liabilities	3.6	0.6
Debt Instrument, Fair Value Disclosure	18.1	18.2
Total Liabilities	21.7	18.8
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Total Derivative Assets	0.0	1.2
Total Derivative Liabilities	3.1	0.0
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.2
Total Derivative Liabilities	0.5	0.6
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities		0.0
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Total Derivative Liabilities		0.0
Equity Securities [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	3.7
Equity Securities [Member] | Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	3.7
Equity Securities [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	3.8	0.0
Equity Securities [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.8	0.0
Debt Securities [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	4.7
Debt Securities [Member] | Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	4.7
Debt Securities [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	4.3	0.0
Debt Securities [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	4.3	0.0
Money Market Funds [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.2	0.1
Money Market Funds [Member] | Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.2	0.1
Money Market Funds [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Hedge Funds [Member]
Total Master Trust Assets, Fair Value		0.0
Hedge Funds [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0
Hedge Funds [Member] | Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Hedge Funds [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	0.4	0.8
Hedge Funds [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.4	0.8
Real Estate Funds [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	0.4
Real Estate Funds [Member] | Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.4
Real Estate Funds [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	0.3	0.0
Real Estate Funds [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.3	0.0
Debt [Member] | Level 1 [Member]
Debt Instrument, Fair Value Disclosure	0.0	0.0
Debt [Member] | Level 2 [Member]
Debt Instrument, Fair Value Disclosure	1,957.2	2,186.6
Debt [Member] | Level 3 [Member]
Debt Instrument, Fair Value Disclosure	18.1	18.2
Fair Value [Member]
Total Master Trust Assets, Fair Value	9.0	9.7
Total Derivative Assets	30.7	14.9
Total Assets	39.7	24.6
Total Derivative Liabilities	27.5	12.2
Total Liabilities	2,002.8	2,217.0
Fair Value [Member] | Forward Contract Power [Member]
Total Derivative Assets	30.5	14.9
Total Derivative Liabilities	27.0	11.1
Fair Value [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.2
Total Derivative Liabilities	0.5	0.6
Fair Value [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities		0.4
Fair Value [Member] | Natural Gas [Member]
Total Derivative Liabilities		0.1
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	9.0	9.7
Total Derivative Assets	30.8	15.1
Total Assets	39.8	24.8
Total Derivative Liabilities	27.5	12.3
Debt Instrument, Fair Value Disclosure	764.2
Total Liabilities	791.7	894.8
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Total Derivative Assets	30.6	15.1
Total Derivative Liabilities	27.0	11.2
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.2
Total Derivative Liabilities	0.5	0.6
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities		0.4
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Total Derivative Liabilities		0.1
Fair Value [Member] | Equity Securities [Member]
Total Master Trust Assets, Fair Value	3.8	3.7
Fair Value [Member] | Equity Securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.8	3.7
Fair Value [Member] | Debt Securities [Member]
Total Master Trust Assets, Fair Value	4.3	4.7
Fair Value [Member] | Debt Securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	4.3	4.7
Fair Value [Member] | Money Market Funds [Member]
Total Master Trust Assets, Fair Value	0.2	0.1
Fair Value [Member] | Money Market Funds [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.2	0.1
Fair Value [Member] | Hedge Funds [Member]
Total Master Trust Assets, Fair Value	0.4	0.8
Fair Value [Member] | Hedge Funds [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.4	0.8
Fair Value [Member] | Real Estate Funds [Member]
Total Master Trust Assets, Fair Value	0.3	0.4
Fair Value [Member] | Real Estate Funds [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.3	0.4
Fair Value [Member] | Debt [Member]
Debt Instrument, Fair Value Disclosure	$ 1,975.3	2,204.8
Fair Value [Member] | Debt [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument, Fair Value Disclosure		$ 882.5