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Allowance for Loan Losses - Private Education Loan Portfolio Stratified by Key Credit Quality Indicators (Detail) - USD ($) $ in Millions | Sep. 30, 2016 | Dec. 31, 2015
--- | --- | ---
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total | $ 25,036 | $ 27,515
Private Education Loans [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Private Education Loans with cosigner | 16,107 | 17,738
Private Education Loans without cosigner | $ 8,929 | $ 9,777
Private Education Loans with cosigner in percent | 64.00% | 64.00%
Private Education Loans without cosigner in percent | 36.00% | 36.00%
Total in percent | 100.00% | 100.00%
School Type/FICO Scores [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total | $ 25,036 | $ 27,515
School Type/FICO Scores [Member] | Private Education Loans [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
School type FICO scores traditional recorded investment | 23,006 | 25,280
School type FICO scores non-traditional recorded investment | $ 2,030 | $ 2,235
School type FICO scores traditional recorded investment, in percent | 92.00% | 92.00%
School type FICO scores non-traditional recorded investment, in percent | 8.00% | 8.00%
Total in percent | 100.00% | 100.00%
Seasoning [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Total | $ 25,036 | $ 27,515
Seasoning [Member] | Private Education Loans [Member] |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |
Seasoning - based on monthly scheduled payments due from 1-12 payments | 1,348 | 1,776
Seasoning - based on monthly scheduled payments due from 13-24 payments | 1,430 | 1,977
Seasoning - based on monthly scheduled payments due from 25-36 payments | 2,234 | 2,982
Seasoning - based on monthly scheduled payments due from 37-48 payments | 3,172 | 3,787
Seasoning - based on monthly scheduled payments due from more than 48 payments | 15,313 | 14,953
Seasoning - based on monthly scheduled payments due from not yet in repayment | $ 1,539 | $ 2,040
Seasoning based on monthly scheduled payments due from 1-12 payments, in percent | 5.00% | 7.00%
Seasoning based on monthly scheduled payments due from 13 - 24 payments, in percent | 6.00% | 7.00%
Seasoning based on monthly scheduled payments due from 25 - 36 payments, in percent | 9.00% | 11.00%
Seasoning based on monthly scheduled payments due from 37 - 48 payments, in percent | 13.00% | 14.00%
Seasoning based on monthly scheduled payments due from more than 48 payments, in percent | 61.00% | 54.00%
Seasoning - based on monthly scheduled payments due from not yet in repayment, in percent | 6.00% | 7.00%
Total in percent | 100.00% | 100.00%

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