Fair Value (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Level 1 [Member]
Total Master Trust Assets, Fair Value	$ 0.1	$ 0.2
Total Derivative Assets	0.0	0.0
Total Assets	0.1	0.2
Total Derivative Liabilities	0.2	0.0
Total Liabilities	0.2	0.0
Level 1 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities	0.0	0.0
Level 1 [Member] | Forward Contract Power [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities	0.0	0.0
Level 1 [Member] | Natural Gas [Member]
Total Derivative Liabilities	0.2
Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.1	0.2
Total Derivative Assets	0.0	0.0
Total Assets	0.1	0.2
Total Derivative Liabilities	0.2	0.0
Total Liabilities	0.2	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	0.0
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] | Natural Gas [Member]
Total Derivative Liabilities	0.2
Level 2 [Member]
Total Master Trust Assets, Fair Value	8.4	8.8
Total Derivative Assets	62.5	30.5
Total Assets	70.9	39.3
Total Derivative Liabilities	41.1	23.9
Total Liabilities	(1,918.0)	1,981.1
Level 2 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities	0.0	0.0
Level 2 [Member] | Forward Contract Power [Member]
Total Derivative Assets	62.5	30.5
Total Derivative Liabilities	41.1	23.9
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	8.4	8.8
Total Derivative Assets	62.7	30.6
Total Assets	71.1	39.4
Total Derivative Liabilities	41.1	23.9
Total Liabilities	788.4	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	0.0
Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Total Derivative Assets	62.7	30.6
Total Derivative Liabilities	41.1	23.9
Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Total Derivative Liabilities	0.0
Level 3 [Member]
Total Derivative Assets	(1.7)	0.2
Total Assets	(1.7)	0.2
Total Derivative Liabilities	2.6	3.6
Total Liabilities	3,938.9	21.7
Level 3 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.1	0.2
Total Derivative Liabilities	0.2	0.5
Level 3 [Member] | Forward Contract Power [Member]
Total Derivative Assets	(1.8)	0.0
Total Derivative Liabilities	2.4	3.1
Level 3 [Member] | Natural Gas [Member]
Total Derivative Liabilities	0.0
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Derivative Assets	(1.6)	0.2
Total Assets	(1.6)	0.2
Total Derivative Liabilities	2.6	3.6
Total Liabilities	20.7	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	0.2	0.5
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Total Derivative Assets	(1.7)	0.0
Total Derivative Liabilities	2.4	3.1
Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Total Derivative Liabilities	0.0
Fair Value [Member]
Total Master Trust Assets, Fair Value	8.5	9.0
Total Derivative Assets	60.8	30.7
Total Assets	69.3	39.7
Total Derivative Liabilities	43.9	27.5
Total Liabilities	2,021.1	2,002.8
Fair Value [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.1	0.2
Total Derivative Liabilities	0.2	0.5
Fair Value [Member] | Forward Contract Power [Member]
Total Derivative Assets	60.7	30.5
Total Derivative Liabilities	43.5	27.0
Fair Value [Member] | Natural Gas [Member]
Total Derivative Liabilities	0.2
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	8.5	9.0
Total Derivative Assets	61.1	30.8
Total Assets	69.6	39.8
Total Derivative Liabilities	43.9	27.5
Total Liabilities	809.3	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	0.2	0.5
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Forward Contract Power [Member]
Total Derivative Assets	61.0	30.6
Total Derivative Liabilities	43.5	27.0
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member] | Natural Gas [Member]
Total Derivative Liabilities	0.2
Money Market Funds [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.1	0.2
Money Market Funds [Member] | Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.1	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] | Fair Value [Member]
Total Master Trust Assets, Fair Value	0.1	0.2
Money Market Funds [Member] | Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.1	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	3.8	3.8
Equity Securities [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.8	3.8
Equity Securities [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	3.8	3.8
Equity Securities [Member] | Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.8	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	3.9	4.3
Debt Securities [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.9	4.3
Debt Securities [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	3.9	4.3
Debt Securities [Member] | Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.9	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	0.3	0.4
Hedge Funds [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.3	0.4
Hedge Funds [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	0.3	0.4
Hedge Funds [Member] | Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.3	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] | 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	(1,959.1)	1,957.2
Debt [Member] | Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt	747.3	746.1
Debt [Member] | Level 3 [Member]
Debt	3,936.3	18.1
Debt [Member] | Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt	18.1	18.1
Debt [Member] | Fair Value [Member]
Debt	1,977.2	1,975.3
Debt [Member] | Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt	$ 765.4	$ 764.2