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Significant Accounting Policies - Deposits (Details) | 12 Months Ended
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Dec. 31, 2021
Accounting Policies [Abstract] |
Period of notification for withdrawal of deposits (less than or equal to) | 7 days

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- Definition Deposits, Period of Notification for Withdrawal + References No definition available. + Details
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Namespace Prefix: | slm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration