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Borrowings - Other Borrowing Sources Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Debt Disclosure [Abstract]
Uncommitted federal funds	$ 125
Lendable value of collateral	$ 2,200	$ 3,300

X

- Definition

Lendable value of collateral

+ References

No definition available.

+ Details

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

X

- Definition

Uncommitted Federal Funds

+ References

No definition available.

+ Details

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

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- References

No definition available.

+ Details

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