v3.25.4

Commitments And Contingent Liabilities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2025	Sep. 30, 2025
Minimum
Unfunded And Commitments To Originate [Line Items]
Fixed expiration of commitments to extend credit (in days)	60 days
Maximum
Unfunded And Commitments To Originate [Line Items]
Fixed expiration of commitments to extend credit (in days)	360 days
Unfunded Commitments, Equity Lines of Credit Including Suspended Accounts
Unfunded And Commitments To Originate [Line Items]
Unfunded commitments on home equity lines of credit (including commitments for suspended accounts)	$ 5,629,816
Loan Sale Commitments | Residential Mortgage
Unfunded And Commitments To Originate [Line Items]
Contractual Obligation	11,298	$ 59,340
Unfunded Loan Commitment
Unfunded And Commitments To Originate [Line Items]
Unfunded commitments on home equity lines of credit (including commitments for suspended accounts)	5,582,424
Unfunded Loan Commitment | Home Equity Line of Credit
Unfunded And Commitments To Originate [Line Items]
Unfunded commitments on home equity lines of credit (including commitments for suspended accounts)	$ 5,574,340
Unfunded Loan Commitment | Home Equity Line of Credit | Maximum
Unfunded And Commitments To Originate [Line Items]
Home equity unfunded commitments expiration period, years	10 years
Loan Purchase Commitments | Residential Mortgage
Unfunded And Commitments To Originate [Line Items]
Contractual Obligation	$ 38,457	$ 28,460

X

- Definition

Fixed Expiration Of Commitments To Extend Credit, Days

+ References

No definition available.

+ Details

Name:	tfsl_FixedExpirationOfCommitmentsToExtendCreditDays
Namespace Prefix:	tfsl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of contractual obligation, including, but not limited to, long-term debt, lease obligation, purchase obligation, and other commitments.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477314/942-235-S99-2

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480738/235-10-S50-4

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(a))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-3

+ Details

Name:	us-gaap_ContractualObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The face amount of financial liabilities, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-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 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 825
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478898/942-825-50-1

+ Details

Name:	us-gaap_FairValueDisclosureOffbalanceSheetRisksFaceAmountLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Period remaining on line of credit facility before it terminates, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- 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

No definition available.

+ Details

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

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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Period Type:

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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Balance Type:
Period Type: