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Allowance for Loan Losses - Additional Information (Detail) $ in Billions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2017 USD ($) Point Loans | Dec. 31, 2016 USD ($)
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Percentage of loans granted forbearance that migrated to TDR classification | 62.00% | 61.00%
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 | $ | $ 2.5 | $ 2.6
Minimum [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Delinquency period (in days) | 212 days |
Minimum [Member] | FICO Score, 600 to 699 [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Original FICO score at for-profit schools to become eligible for non-traditional loans | 640 |
Maximum [Member] | FICO Score, 600 to 699 [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Original FICO score at for-profit schools to become eligible for non-traditional loans | 670 |
Private Education Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Number of classes of loans | Loans | 2 |

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- Definition Original Fico score at for profit schools to become eligible for non traditional loans. + 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 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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