Additional Proceeds from Sale of Debt Securities, Available-for-sale

No definition available.

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Namespace Prefix:	slm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Estimated weighted average life of student loans.

+ References

No definition available.

+ Details

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- Definition

Lendable value of collateral

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Loans Pledged As Collateral, Capitalized Interest

+ References

No definition available.

+ Details

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Namespace Prefix:	slm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Loans Pledged As Collateral, Principal Amount

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Loans Securitized or Asset Backed Financing Arrangement Ownership Interest Percentage

+ References

No definition available.

+ Details

Name:	slm_LoansSecuritizedOrAssetBackedFinancingArrangementOwnershipInterestPercentage
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Balance Type:	na
Period Type:	instant

- Definition

Number Of Loans Securitized

+ References

No definition available.

+ Details

Name:	slm_NumberOfLoansSecuritized
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Balance Type:	na
Period Type:	duration

- Definition

Residual Interest Percentage Of Facility Trust

+ References

No definition available.

+ Details

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Data Type:	dtr-types:percentItemType
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Period Type:	instant

- Definition

Uncommitted Federal Funds

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Vertical Risk Retention, Percentage

+ References

No definition available.

+ Details

Name:	slm_VerticalRiskRetentionPercentage
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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Principal amount of transferred financial assets in which the transferor has continuing involvement with the assets underlying the transaction. Continuing involvement includes, but is not limited to, servicing, recourse, and restrictions on transferor's interests in transferred financial assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-URI https://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

+ Details

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

- Definition

Amount of realized gain on 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/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27357-111563

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

This is the principal amount outstanding for loans which are in the process of being securitized as of the date of the statement of financial position (across all types of loans).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

+ Details

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

- Definition

The cash inflow from the issuance of long-term debt that is not secured by collateral. Excludes proceeds from tax exempt unsecured debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3255-108585

+ Details

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

- Definition

Amount of cash inflow from sale 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26853-111562

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 11
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3151-108585

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3179-108585

+ Details

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

- Definition

Fair value of the securities pledged as collateral against securities loaned.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 12
-URI https://asc.fasb.org/extlink&oid=99393222&loc=SL20226013-175313

+ Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_DebtInstrumentAxis=slm_ABCPBorrowingsMember
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- Details

Name:	us-gaap_DebtInstrumentAxis=slm_A2022AMember
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- Details

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

- Details

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- Details

Name:	us-gaap_DebtInstrumentAxis=slm_SMBPrivateEducationLoanTrust2022CMember
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- Details

Name:	us-gaap_VariableRateAxis=us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
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Borrowings - Narrative (Details)				9 Months Ended				12 Months Ended
Borrowings - Narrative (Details)	Aug. 09, 2022 USD ($)	May 27, 2022 USD ($) Rate	Mar. 16, 2022 USD ($) Rate	Sep. 30, 2022 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2022 USD ($) SecurityLoan	Sep. 30, 2022 USD ($) Rate	Dec. 31, 2021 USD ($)	May 17, 2022 USD ($)
Line of Credit Facility [Line Items]
Secured borrowings outstanding				$ 5,522,311,000	$ 5,522,311,000	$ 5,522,311,000	$ 5,522,311,000	$ 5,930,990,000
Estimated weighted average life of student loans				5 years				4 years 8 months 12 days
Number of loans securitized \| SecurityLoan						1
Vertical risk retention interest					5.00%		5.00%
Uncommitted federal funds				$ 125,000,000	$ 125,000,000	$ 125,000,000	$ 125,000,000
Lendable value of collateral				2,600,000,000	2,600,000,000	2,600,000,000	2,600,000,000	$ 3,300,000,000
Secured borrowings
Line of Credit Facility [Line Items]
Secured borrowings outstanding				4,534,129,000	4,534,129,000	4,534,129,000	4,534,129,000	4,944,852,000
ABCP borrowings \| Secured borrowings
Line of Credit Facility [Line Items]
Secured borrowing facility maximum borrowing capacity									$ 2,000,000,000
Residual interest percentage of facility trust									100.00%
Secured borrowings outstanding				0	0	0	0	$ 0
2022-A
Line of Credit Facility [Line Items]
Vertical risk retention interest \| Rate			5.00%
2022-A \| Student Loan
Line of Credit Facility [Line Items]
Private education loans sold			$ 973,000,000
Additional net proceeds from sales of loans held for investment, capitalized interest			95,000,000
Gain on sale			$ 10,000,000
2022-B
Line of Credit Facility [Line Items]
Vertical risk retention interest \| Rate		5.00%
2022-B \| Student Loan
Line of Credit Facility [Line Items]
Private education loans sold		$ 2,000,000,000
Additional net proceeds from sales of loans held for investment, capitalized interest		107,000,000
Gain on sale		$ 11,000,000
2022-C
Line of Credit Facility [Line Items]
Private education loan term accounted for as a secured financing	$ 575,000,000
Loans sold to third parties	$ 575,000,000
Ownership interest percentage on asset-backed financing	100.00%
Unsecured debt issued	$ 575,000,000
Estimated weighted average life of student loans	4 years 8 months 8 days
Loans pledged as collateral				658,000,000	658,000,000	658,000,000	658,000,000
Principal amount of collateral				613,000,000	613,000,000	613,000,000	613,000,000
Capitalized interest				$ 45,000,000	$ 45,000,000	$ 45,000,000	$ 45,000,000
2022-C \| Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.76%