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Allowance for Loan Losses - Average Recorded Investment and Interest Income Recognized for TDR (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired financing receivable, Average Recorded Investment | $ 10,769 | $ 10,444 | $ 10,721 | $ 10,396
Impaired financing receivable, Interest Income Recognized | 167 | 163 | 497 | 488
Private Education Loans - Traditional [Member] |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired financing receivable, Average Recorded Investment | 9,367 | 8,988 | 9,303 | 8,930
Impaired financing receivable, Interest Income Recognized | 140 | 134 | 416 | 402
Private Education Loans - Non-Traditional [Member] |  |  |  |
Financing Receivable, Impaired [Line Items] |  |  |  |
Impaired financing receivable, Average Recorded Investment | 1,402 | 1,456 | 1,418 | 1,466
Impaired financing receivable, Interest Income Recognized | $ 27 | $ 29 | $ 81 | $ 86

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- Definition Average amount of investment of impaired financing receivables with related allowance for credit losses and without a 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 (c)(1) -URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5258-111524 + Details
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