Equity (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
Equity (Details) - USD ($) $ in Millions	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024	Apr. 09, 2025	Apr. 04, 2025	Dec. 31, 2024	Dec. 31, 2023
Stockholders' Equity Note Disclosure							8. EQUITY Transactions with Holders of Redeemable Stock of Subsidiaries On April 4, 2025, DPL sold an aggregate indirect equity interest in AES Ohio of approximately 30% to Astrid Holdings LP, a wholly-owned subsidiary of CDPQ, for total proceeds of approximately $544 million, resulting in an increase to Redeemable stock of subsidiaries of $537.5 million, net of transaction costs on the Condensed Consolidated Balance Sheets. The shareholders' agreements contain certain redemption features that, while not currently in effect, are not solely in DPL's control. As a result, the noncontrolling ownership interest is considered temporary equity. The Company has concluded that the likelihood of an event that would allow CDPQ to redeem its interest under the terms of the shareholders' agreements is remote, but would require redemption at fair value. Therefore, as of September 30, 2025, the noncontrolling ownership interest is not probable of becoming redeemable and subsequent adjustments to the carrying value were not required. The transaction also resulted in reclassification of $2.7 million of pension related AOCL to Member's equity. As DPL maintained control after the transaction, AES Ohio continues to be consolidated by DPL. On April 9, 2025, CDPQ made capital contributions totaling $45.0 million as part of a capital call primarily for funding needs related to AES Ohio’s capital expenditure program. The capital contributions were made on a proportional share basis and, therefore, did not change CDPQ’s or DPL’s ownership interests in Ohio Investments or Ohio Holdings. Other Paid-in Capital During the nine months ended September 30, 2024, DPL received $200.0 million in equity contributions from AES. DPL then made the same investments in AES Ohio. The proceeds from these equity contributions allow AES Ohio to seek to improve its infrastructure and modernize its grid while maintaining liquidity.
Cash Contribution from Parent Company								$ 200.0
Proceeds from Contributions from Parent					$ 130.0		$ 0.0	200.0
Proceeds from Issuance of Redeemable Convertible Preferred Stock							539.7	0.0
Non-cash capital contribution	$ 0.0			$ 70.0
Stockholders' Equity, Other				(0.1)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	401.5	$ 393.4	$ 364.8	371.6	291.3	$ 151.3	401.5	371.6			$ 362.1	$ 148.9
Members' Equity	3,048.4	3,048.4					3,048.4
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest	0.1	0.2
Other Comprehensive Income (Loss), Net of Tax	(0.1)			(0.1)	(0.2)	(0.2)	(0.1)	(0.5)
Proceeds from Issuance of Common Stock		45.0					45.0	0.0
Proceeds from Noncontrolling Interests		537.5
Net Income (Loss) Attributable to Parent	8.3	0.7	2.7	10.3	10.2	2.6	11.7	23.1
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest	(5.1)	(1.6)		0.0			(6.7)	0.0
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent	(0.2)	(0.2)
Redeemable Noncontrolling Interest, Equity, Carrying Amount	588.7	584.3					588.7				0.0
Equity
Members' Equity		(2.7)
AOCI Attributable to Parent [Member]
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent		$ 2.7
Common Stock [Member]
Shares, Issued		1
Equity
Members' Equity		$ 3,040.5
Operating Segments [Member] \| Utility [Member]
Net Income (Loss) Attributable to Parent				12.5				37.0
CDPQ
General Partners' Contributed Capital									$ 45.0
Other Additional Capital [Member]
Proceeds from Contributions from Parent				70.0	130.0
Stockholders' Equity, Other				0.1
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	0.0	0.0	3,040.5	3,040.5	2,970.4	2,840.4	0.0	3,040.5			3,040.5	2,840.4
Common Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0	$ 0.0			$ 0.0	$ 0.0
Shares, Issued	0	0	1	1	1	1	0	1			1	1
Subsidiaries [Member]
CDPQ Investment total										$ 544.0
CDPQ Investment percent										30.00%

DPL LLC 10-Q