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Allowance for Loan Losses - Additional Information (Detail) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2015 USD ($) | Mar. 31, 2015 | Sep. 30, 2016 USD ($) Point Loans | Sep. 30, 2015 USD ($) | Dec. 31, 2015 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Maximum original FICO score at for-profit schools to become eligible for non-traditional loans | Point |  |  | 670 |  |
Maximum original FICO score at not-for-profit schools to become eligible for non-traditional loans | Point |  |  | 640 |  |
Net adjustment resulting from the change in the charge-off rate |  |  |  | $ 330 |
Percentage of loans granted forbearance that migrated to TDR classification |  |  | 59.00% |  | 56.00%
Payment default period for TDRs |  |  | 60 days past due |  |
Interest Rate Reduction [Member] |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
TDR loans, Unpaid Principal Balance |  |  | $ 2,700 |  | $ 2,500
Minimum [Member] |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Delinquency period (in days) |  |  |  |  | 212 days
Private Education Loans [Member] |  |  |  |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |  |  |  |
Number of classes of loans | Loans |  |  | 2 |  |
Portion of loan amount charged off at default | 79.00% | 73.00% |  |  |
Net adjustment resulting from the change in the charge-off rate | $ 330 |  |  | $ 330 |
Loans default recovery rate | 21.00% |  |  |  |

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- Definition Maximum original FICO score at for-profit schools to become eligible for non-traditional loans. + References No definition available. + Details
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- Definition Maximum original FICO score at not-for-profit schools to become eligible for non-traditional loans. + References No definition available. + Details
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- Definition Number of classes of loans. + References No definition available. + Details
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- Definition Payment default period for troubled debt restructurings. + References No definition available. + Details
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- Definition Percentage of loans granted forbearance that migrated to troubled debt restructuring classification. + References No definition available. + Details
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- Definition Portion of loan amount charged off at default. + References No definition available. + Details
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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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- Definition Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524 + Details
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- Definition Threshold period past due for financing receivable to write off as uncollectible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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