Fair Value (Fair Value Of Assets And Liabilities Measured On Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2019
Assets:
Available-for-sale Securities	$ 514,330	$ 547,864
Derivative		44
Liabilities:
Mortgage loans held for sale	51,446	3,706
REMIC's
Assets:
Available-for-sale Securities	507,940	541,042
Fannie Mae Certificates
Assets:
Available-for-sale Securities	6,390	6,822
Subject To Pending Agency Contracts
Liabilities:
Mortgage loans held for sale	45,231	0
Quoted Prices In Active Markets For Identical Assets (Level 1)
Assets:
Available-for-sale Securities	0	0
Derivative		0
Liabilities:
Mortgage loans held for sale	0	0
Quoted Prices In Active Markets For Identical Assets (Level 1) \| Subject To Pending Agency Contracts
Liabilities:
Mortgage loans held for sale	0
Significant Other Observable Inputs (Level 2)
Assets:
Available-for-sale Securities	514,330	547,864
Derivative		0
Liabilities:
Mortgage loans held for sale	51,446	3,706
Significant Other Observable Inputs (Level 2) \| Subject To Pending Agency Contracts
Liabilities:
Mortgage loans held for sale	45,231
Significant Unobservable Inputs (Level 3)
Assets:
Available-for-sale Securities	0	0
Derivative		44
Liabilities:
Mortgage loans held for sale	0	0
Significant Unobservable Inputs (Level 3) \| Subject To Pending Agency Contracts
Liabilities:
Mortgage loans held for sale	0
Fair Value, Measurements, Recurring
Assets:
Total	560,255	547,908
Liabilities:
Total	0	0
Fair Value, Measurements, Recurring \| Interest Rate Lock Commitments
Assets:
Derivative	681	44
Fair Value, Measurements, Recurring \| Forward Commitments For Sale Of Mortgage Loans
Assets:
Derivative	13
Fair Value, Measurements, Recurring \| REMIC's
Assets:
Available-for-sale Securities	507,940	541,042
Fair Value, Measurements, Recurring \| Fannie Mae Certificates
Assets:
Available-for-sale Securities	6,390	6,822
Fair Value, Measurements, Recurring \| Quoted Prices In Active Markets For Identical Assets (Level 1)
Assets:
Total	0	0
Fair Value, Measurements, Recurring \| Quoted Prices In Active Markets For Identical Assets (Level 1) \| Interest Rate Lock Commitments
Assets:
Derivative	0	0
Fair Value, Measurements, Recurring \| Quoted Prices In Active Markets For Identical Assets (Level 1) \| Forward Commitments For Sale Of Mortgage Loans
Assets:
Derivative	0
Fair Value, Measurements, Recurring \| Quoted Prices In Active Markets For Identical Assets (Level 1) \| REMIC's
Assets:
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring \| Quoted Prices In Active Markets For Identical Assets (Level 1) \| Fannie Mae Certificates
Assets:
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets:
Total	559,574	547,864
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Interest Rate Lock Commitments
Assets:
Derivative	0	0
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Forward Commitments For Sale Of Mortgage Loans
Assets:
Derivative	13
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| REMIC's
Assets:
Available-for-sale Securities	507,940	541,042
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2) \| Fannie Mae Certificates
Assets:
Available-for-sale Securities	6,390	6,822
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets:
Total	681	44
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| Interest Rate Lock Commitments
Assets:
Derivative	681	44
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| Forward Commitments For Sale Of Mortgage Loans
Assets:
Derivative	0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| REMIC's
Assets:
Available-for-sale Securities	0	0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3) \| Fannie Mae Certificates
Assets:
Available-for-sale Securities	$ 0	$ 0

No definition available.

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

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

No definition available.

+ Details

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

- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Fair value of financial and nonfinancial obligations.

+ References

+ Details

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

- Definition

Fair value portion of mortgage loans held-for-sale.

+ References

No definition available.

+ Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=tfsl_LoansHeldForSaleSubjectToPendingAgencyContractsMember
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_FairValueByAssetClassAxis=us-gaap_InterestRateLockCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=tfsl_ForwardCommitmentsForSaleOfMortgageLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: