Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Inputs, Level 1 [Member]
Total Assets	$ 7.5	$ 0.4
Total Liabilities	0.0	0.0
Fair Value, Inputs, Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets	7.5	0.4
Debt Instrument, Fair Value Disclosure		0.0
Total Liabilities	0.0
Fair Value, Inputs, Level 2 [Member]
Total Assets	0.0	9.0
Total Liabilities	1,376.4	1,502.5
Fair Value, Inputs, Level 2 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets	0.0	9.0
Debt Instrument, Fair Value Disclosure		625.4
Total Liabilities	610.9
Fair Value, Inputs, Level 3 [Member]
Total Assets	0.0	0.0
Total Liabilities	17.0	17.2
Fair Value, Inputs, Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets	0.0	0.0
Debt Instrument, Fair Value Disclosure		17.2
Total Liabilities	17.0
Money Market Funds [Member] \| Fair Value, Inputs, Level 1 [Member]
Total Master Trust Assets, Fair Value	0.5	0.4
Money Market Funds [Member] \| Fair Value, Inputs, Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.5	0.4
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
Money Market Funds [Member] \| Fair Value, Inputs, Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Mutual Fund \| Fair Value, Inputs, Level 1 [Member]
Total Master Trust Assets, Fair Value	7.0	0.0
Mutual Fund \| Fair Value, Inputs, Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	7.0	0.0
Mutual Fund \| Fair Value, Inputs, Level 2 [Member]
Total Master Trust Assets, Fair Value	0.0	9.0
Mutual Fund \| Fair Value, Inputs, Level 2 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	9.0
Mutual Fund \| Fair Value, Inputs, Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Mutual Fund \| Fair Value, Inputs, Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Carrying Value [Member] \| Debt [Member]
Long-term Debt	1,535.9	1,395.5
Carrying Value [Member] \| Debt [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Long-term Debt	712.7	574.3
Fair Value [Member]
Total Assets	7.5	9.4
Total Liabilities	1,393.4	1,519.7
Fair Value [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Assets	7.5	9.4
Total Liabilities	627.9
Fair Value [Member] \| Money Market Funds [Member]
Total Master Trust Assets, Fair Value	0.5	0.4
Fair Value [Member] \| Money Market Funds [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.5	0.4
Fair Value [Member] \| Debt [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument, Fair Value Disclosure		642.6
Fair Value [Member] \| Mutual Fund
Total Master Trust Assets, Fair Value	7.0	9.0
Fair Value [Member] \| Mutual Fund \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	$ 7.0	$ 9.0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

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Fair value of financial and nonfinancial obligations.

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Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

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