Other Financing Liabilities, at Fair Value – Schedule of Results of Operations in Connection With MSR Transfer Agreements that Do Not Qualify for Sale Accounting (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Related Party Transaction [Line Items]
Proceeds from Collection of Loans Receivable	$ 32.6	$ 36.9	$ 64.9	$ 73.6
Less: Subservicing fee retained by Onity	(5.5)	(6.8)	(11.4)	(13.9)
Ancillary and other settlement	2.9	3.0	5.2	5.3
MSR Pledged liability expense	43.0	46.1	84.9	91.0
Financing Liability Mortgage Servicing Rights Pledged [Member]
Related Party Transaction [Line Items]
MSR Pledged liability expense	30.0	33.1	58.8	65.0
Financing Liability Excess Servicing Spread [Member]
Related Party Transaction [Line Items]
MSR Pledged liability expense	13.0	13.0	26.1	26.1
MSR Asset Vehicle LLC
Related Party Transaction [Line Items]
Proceeds from Collection of Loans Receivable	13.3	17.8	26.7	35.8
Less: Subservicing fee retained by Onity	(1.8)	(2.3)	(3.7)	(4.9)
Ancillary and other settlement	(0.1)	(0.2)	(0.2)	(0.3)
MSR Pledged liability expense	11.3	15.3	22.8	30.7
Rithm Capital Corp . and others
Related Party Transaction [Line Items]
Proceeds from Collection of Loans Receivable	19.3	19.1	38.2	37.8
Less: Subservicing fee retained by Onity	(3.6)	(4.4)	(7.7)	(9.0)
Ancillary and other settlement	3.0	3.1	5.4	5.5
MSR Pledged liability expense	$ 18.7	$ 17.8	$ 36.0	$ 34.3

Ancillary fee/income and other settlement (incl. expense reimbursement)

No definition available.

Name:	onit_AncillaryAndOtherSettlement
Namespace Prefix:	onit_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Bank Servicing Fees Retained

+ References

No definition available.

+ Details

Name:	onit_BankServicingFeesRetained
Namespace Prefix:	onit_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents interest incurred for borrowed money which was used to produce goods or render services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

+ Details

Name:	us-gaap_FinancingInterestExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow associated with the collection, including prepayments, of loans receivable issued for financing of goods and services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-12

+ Details

Name:	us-gaap_ProceedsFromCollectionOfLoansReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c)(2)(i))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c)(2)(ii))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

+ Details

Name:	us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=onit_FinancingLiabilityMortgageServicingRightsPledgedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=onit_FinancingLiabilityExcessServicingSpreadMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=onit_MSRAssetVehicleLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=onit_RithmCapitalCorpAndOthersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: