Cash and Cash Equivalents in Investment Securities, Fair Value Disclosure

No definition available.

Name:	omf_CashAndCashEquivalentsInInvestmentSecuritiesFairValueDisclosure
Namespace Prefix:	omf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the fair value of cash and cash equivalents in mutual funds.

+ References

No definition available.

+ Details

Name:	omf_CashAndCashEquivalentsInMutualFundsFairValueDisclosure
Namespace Prefix:	omf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the fair value of restricted cash in mutual funds.

+ References

No definition available.

+ Details

Name:	omf_RestrictedCashInMutualFundsFairValueDisclosure
Namespace Prefix:	omf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of asset recognized for present right to economic benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 100
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-100

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-28

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-11

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-11

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-10

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2E

+ Details

Name:	us-gaap_InvestmentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of cash and cash equivalent restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposit with financial institution, and account with general characteristic of demand deposit. Cash equivalent includes, but is not limited to, short-term, highly liquid investment that is both readily convertible to known amount of cash and so near maturity that it presents insignificant risk of change in value because of change in interest rate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(1))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482913/230-10-50-8

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(1)(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-4

+ Details

Name:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(4))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483467/210-10-45-1

+ Details

Name:	us-gaap_TradingSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CollateralizedDebtObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_BondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_PreferredStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Fair Value Measurements - Schedule of Assets at Fair Value Recurring Basis (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024	Jun. 30, 2024
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	$ 1,623	$ 1,539
Other securities	60	68
Restricted cash and restricted cash equivalents	742	684	$ 630
U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	31	12
Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	56	61
Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	39	9
Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	152	155
Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	1,057	1,021
RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	188	184
CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	23	27
CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	77	70
Level 1
Investments, Debt and Equity Securities [Abstract]
Total investment securities	56	54
Restricted cash and restricted cash equivalents	742	677
Level 2
Investments, Debt and Equity Securities [Abstract]
Total investment securities	1,626	1,550
Restricted cash and restricted cash equivalents	0	7
Level 3
Investments, Debt and Equity Securities [Abstract]
Total investment securities	1	3
Restricted cash and restricted cash equivalents	0	0
Fair Value, Measurements, Recurring
Assets
Cash equivalents in mutual funds	79	55
Cash equivalents in securities		5
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	1,623	1,539
Other securities	60	68
Total investment securities	1,683	1,607
Restricted cash equivalents in mutual funds	726	672
Restricted cash and restricted cash equivalents		7
Total	2,488	2,346
Fair Value, Measurements, Recurring \| Total bonds
Investments, Debt and Equity Securities [Abstract]
Other securities	9	18
Fair Value, Measurements, Recurring \| U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	31	12
Fair Value, Measurements, Recurring \| Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	56	61
Fair Value, Measurements, Recurring \| Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	39	9
Fair Value, Measurements, Recurring \| Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	152	155
Fair Value, Measurements, Recurring \| Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	1,057	1,021
Other securities	3	4
Fair Value, Measurements, Recurring \| RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	188	184
Fair Value, Measurements, Recurring \| CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	23	27
Fair Value, Measurements, Recurring \| CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	77	70
Other securities	6	14
Fair Value, Measurements, Recurring \| Preferred stock
Investments, Debt and Equity Securities [Abstract]
Other securities	13	13
Fair Value, Measurements, Recurring \| Common stock
Investments, Debt and Equity Securities [Abstract]
Other securities	38	37
Fair Value, Measurements, Recurring \| Level 1
Assets
Cash equivalents in mutual funds	79	55
Cash equivalents in securities		0
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	6	6
Other securities	50	48
Total investment securities	56	54
Restricted cash equivalents in mutual funds	726	672
Restricted cash and restricted cash equivalents		0
Total	861	781
Fair Value, Measurements, Recurring \| Level 1 \| Total bonds
Investments, Debt and Equity Securities [Abstract]
Other securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	6	6
Other securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Other securities	0	0
Fair Value, Measurements, Recurring \| Level 1 \| Preferred stock
Investments, Debt and Equity Securities [Abstract]
Other securities	13	13
Fair Value, Measurements, Recurring \| Level 1 \| Common stock
Investments, Debt and Equity Securities [Abstract]
Other securities	37	35
Fair Value, Measurements, Recurring \| Level 2
Assets
Cash equivalents in mutual funds	0	0
Cash equivalents in securities		5
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	1,617	1,532
Other securities	9	18
Total investment securities	1,626	1,550
Restricted cash equivalents in mutual funds	0	0
Restricted cash and restricted cash equivalents		7
Total	1,626	1,562
Fair Value, Measurements, Recurring \| Level 2 \| Total bonds
Investments, Debt and Equity Securities [Abstract]
Other securities	9	18
Fair Value, Measurements, Recurring \| Level 2 \| U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	31	12
Fair Value, Measurements, Recurring \| Level 2 \| Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	56	61
Fair Value, Measurements, Recurring \| Level 2 \| Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	39	9
Fair Value, Measurements, Recurring \| Level 2 \| Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	152	155
Fair Value, Measurements, Recurring \| Level 2 \| Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	1,051	1,014
Other securities	3	4
Fair Value, Measurements, Recurring \| Level 2 \| RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	188	184
Fair Value, Measurements, Recurring \| Level 2 \| CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	23	27
Fair Value, Measurements, Recurring \| Level 2 \| CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	77	70
Other securities	6	14
Fair Value, Measurements, Recurring \| Level 2 \| Preferred stock
Investments, Debt and Equity Securities [Abstract]
Other securities	0	0
Fair Value, Measurements, Recurring \| Level 2 \| Common stock
Investments, Debt and Equity Securities [Abstract]
Other securities	0	0
Fair Value, Measurements, Recurring \| Level 3
Assets
Cash equivalents in mutual funds	0	0
Cash equivalents in securities		0
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	1
Other securities	1	2
Total investment securities	1	3
Restricted cash equivalents in mutual funds	0	0
Restricted cash and restricted cash equivalents		0
Total	1	3
Fair Value, Measurements, Recurring \| Level 3 \| Total bonds
Investments, Debt and Equity Securities [Abstract]
Other securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Obligations of states, municipalities, and political subdivisions
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Commercial paper
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Non-U.S. government and government sponsored entities
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Corporate debt
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	1
Other securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| RMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| CMBS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| CDO/ABS
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities	0	0
Other securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Preferred stock
Investments, Debt and Equity Securities [Abstract]
Other securities	0	0
Fair Value, Measurements, Recurring \| Level 3 \| Common stock
Investments, Debt and Equity Securities [Abstract]
Other securities	$ 1	$ 2