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Commitments and Contingencies - Additional Information (Detail) - USD ($) |  | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
May 13, 2014 | Sep. 30, 2016 | Dec. 31, 2014 | Dec. 31, 2013
Loss Contingencies [Line Items] |  |  |  |
Civil monetary penalties | $ 3,300,000 |  |  |
Establishment of a restitution reserve |  | $ 30,000,000 |  |
Separation and distribution agreement date |  | Apr. 28, 2014 |  |
Estimated amount of credits for similar assessed late fees |  | $ 42,000,000 |  |
Total reserves established during year |  |  | $ 177,000,000 | $ 177,000,000
Indemnification Matters [Member] | SLM BankCo [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Reserve for estimated amounts and costs incurred |  | $ 0 |  |
DOJ Order [Member] |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Civil monetary penalties |  |  | 55,000 |
Settlement fund under DOJ |  |  | $ 60,000,000 |

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- 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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- Details
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