Fair Value (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Fair Value (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unrealized Gain (Loss) on Investments	$ 0.3	$ 0.0	$ 0.2	$ 0.3
Subsidiaries [Member] \| Level 1 [Member] \| Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	0.6		0.6		$ 0.4
Subsidiaries [Member] \| Level 2 [Member] \| Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	0.0		0.0		0.0
Subsidiaries [Member] \| Level 3 [Member] \| Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	0.0		0.0		0.0
Estimate of Fair Value Measurement [Member] \| Subsidiaries [Member] \| Money Market Funds [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Investments, Fair Value Disclosure	$ 0.6		$ 0.6		$ 0.4

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

DPL LLC 10-Q