Fair Value (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Level 1 [Member]
Total Master Trust Assets, Fair Value	$ 0.3	$ 0.2
Total Derivative Assets	0.3	0.0
Total Assets	0.6	0.2
Total Derivative Liabilities	0.0	0.0
Total Liabilities	0.0	0.0
Level 1 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities		0.0
Level 1 [Member] | Natural Gas Futures [Member]
Total Derivative Assets	0.3
Level 1 [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]
Total Master Trust Assets, Fair Value	0.3	0.2
Total Derivative Assets	0.3	0.0
Total Assets	0.6	0.2
Total Derivative Liabilities	0.0	0.0
Total Liabilities	0.0	0.0
Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities		0.0
Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas Futures [Member]
Total Derivative Assets	0.3
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 2 [Member]
Total Master Trust Assets, Fair Value	8.3	8.8
Total Derivative Assets	38.6	30.5
Total Assets	46.9	39.3
Total Derivative Liabilities	38.9	23.9
Total Liabilities	1,933.3	1,981.1
Level 2 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities		0.0
Level 2 [Member] | Natural Gas Futures [Member]
Total Derivative Assets	0.0
Level 2 [Member] | Forward Contract Power [Member]
Total Derivative Assets	38.6	30.5
Total Derivative Liabilities	38.9	23.9
Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	8.3	8.8
Total Derivative Assets	38.7	30.6
Total Assets	47.0	39.4
Total Derivative Liabilities	39.0	23.9
Total Liabilities	785.3	770.0
Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities		0.0
Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas Futures [Member]
Total Derivative Assets	0.0
Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Total Derivative Assets	38.7	30.6
Total Derivative Liabilities	39.0	23.9
Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Total Derivative Assets	0.8	0.2
Total Assets	0.8	0.2
Total Derivative Liabilities	6.3	3.6
Total Liabilities	24.3	21.7
Level 3 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.1	0.2
Total Derivative Liabilities		0.5
Level 3 [Member] | Natural Gas Futures [Member]
Total Derivative Assets	0.0
Level 3 [Member] | Forward Contract Power [Member]
Total Derivative Assets	0.7	0.0
Total Derivative Liabilities	6.3	3.1
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Total Derivative Assets	0.8	0.2
Total Assets	0.8	0.2
Total Derivative Liabilities	6.3	3.6
Total Liabilities	24.3	21.7
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.1	0.2
Total Derivative Liabilities		0.5
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas Futures [Member]
Total Derivative Assets	0.0
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Total Derivative Assets	0.7	0.0
Total Derivative Liabilities	6.3	3.1
Fair Value [Member]
Total Master Trust Assets, Fair Value	8.6	9.0
Total Derivative Assets	39.7	30.7
Total Assets	48.3	39.7
Total Derivative Liabilities	45.2	27.5
Total Liabilities	1,957.6	2,002.8
Fair Value [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.1	0.2
Total Derivative Liabilities		0.5
Fair Value [Member] | Natural Gas Futures [Member]
Total Derivative Assets	0.3
Fair Value [Member] | Forward Contract Power [Member]
Total Derivative Assets	39.3	30.5
Total Derivative Liabilities	45.2	27.0
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	8.6	9.0
Total Derivative Assets	39.8	30.8
Total Assets	48.4	39.8
Total Derivative Liabilities	45.3	27.5
Total Liabilities	809.6	791.7
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.1	0.2
Total Derivative Liabilities		0.5
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas Futures [Member]
Total Derivative Assets	0.3
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Total Derivative Assets	39.4	30.6
Total Derivative Liabilities	45.3	27.0
Money Market Funds [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.3	0.2
Money Market Funds [Member] | Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.3	0.2
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
Money Market Funds [Member] | Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] | Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	0.3	0.2
Money Market Funds [Member] | Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.3	0.2
Equity Securities [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Equity Securities [Member] | Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Equity Securities [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	3.5	3.8
Equity Securities [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.5	3.8
Equity Securities [Member] | Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Equity Securities [Member] | Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Equity Securities [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	3.5	3.8
Equity Securities [Member] | Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.5	3.8
Debt Securities [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt Securities [Member] | Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt Securities [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	4.2	4.3
Debt Securities [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	4.2	4.3
Debt Securities [Member] | Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt Securities [Member] | Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt Securities [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	4.2	4.3
Debt Securities [Member] | Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	4.2	4.3
Hedge Funds [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	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	0.2	0.4
Hedge Funds [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.2	0.4
Hedge Funds [Member] | Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Hedge Funds [Member] | Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Hedge Funds [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	0.2	0.4
Hedge Funds [Member] | Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.2	0.4
Real Estate Funds [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Real Estate Funds [Member] | Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Real Estate Funds [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	0.4	0.3
Real Estate Funds [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.4	0.3
Real Estate Funds [Member] | Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Real Estate Funds [Member] | Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Real Estate Funds [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	0.4	0.3
Real Estate Funds [Member] | Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.4	0.3
Debt [Member] | Level 1 [Member]
Debt	0.0	0.0
Debt [Member] | Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt	0.0	0.0
Debt [Member] | Level 2 [Member]
Debt	1,894.4	1,957.2
Debt [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt	746.3	746.1
Debt [Member] | Level 3 [Member]
Debt	18.0	18.1
Debt [Member] | Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt	18.0	18.1
Debt [Member] | Fair Value [Member]
Debt	1,912.4	1,975.3
Debt [Member] | Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt	$ 764.3	$ 764.2