Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Inputs, Level 1 [Member]
Total Assets	$ 0.4	$ 0.3
Total Liabilities	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets	0.4	0.3
Debt Instrument, Fair Value Disclosure		0.0
Total Liabilities	0.0	0.0
Fair Value, Inputs, Level 2 [Member]
Total Assets	9.0	8.6
Total Liabilities	1,502.5	1,554.2
Fair Value, Inputs, Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets	9.0	8.6
Debt Instrument, Fair Value Disclosure		638.6
Total Liabilities	625.4	638.6
Fair Value, Inputs, Level 3 [Member]
Total Assets	0.0	0.0
Total Liabilities	17.2	17.4
Fair Value, Inputs, Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets		0.0
Debt Instrument, Fair Value Disclosure		17.4
Total Liabilities	17.2	17.4
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Master Trust Assets, Fair Value	5.1	4.5
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	5.1	4.5
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Total Master Trust Assets, Fair Value	3.9	4.1
Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.9	4.1
Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Total Master Trust Assets, Fair Value	0.4	0.3
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.4	0.3
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] | Fair Value, Inputs, 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, Inputs, Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt [Member] | Fair Value, Inputs, Level 1 [Member]
Debt Instrument, Fair Value Disclosure	0.0	0.0
Debt [Member] | Fair Value, Inputs, Level 1 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument, Fair Value Disclosure	0.0
Debt [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Instrument, Fair Value Disclosure	1,502.5	1,554.2
Debt [Member] | Fair Value, Inputs, Level 2 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument, Fair Value Disclosure	625.4
Debt [Member] | Fair Value, Inputs, Level 3 [Member]
Debt Instrument, Fair Value Disclosure	17.2	17.4
Debt [Member] | Fair Value, Inputs, Level 3 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument, Fair Value Disclosure	17.2
Fair Value [Member]
Total Assets	9.4	8.9
Total Liabilities	1,519.7	1,571.6
Fair Value [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets	9.4	8.9
Total Liabilities	642.6	656.0
Fair Value [Member] | Equity Securities [Member]
Total Master Trust Assets, Fair Value	5.1	4.5
Fair Value [Member] | Equity Securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	5.1	4.5
Fair Value [Member] | Debt Securities [Member]
Total Master Trust Assets, Fair Value	3.9	4.1
Fair Value [Member] | Debt Securities [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.9	4.1
Fair Value [Member] | Money Market Funds [Member]
Total Master Trust Assets, Fair Value	0.4	0.3
Fair Value [Member] | Money Market Funds [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.4	0.3
Fair Value [Member] | Debt [Member]
Debt Instrument, Fair Value Disclosure	1,519.7	1,571.6
Fair Value [Member] | Debt [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument, Fair Value Disclosure	$ 642.6	$ 656.0