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Allowance for Loan Losses - Loans Modified Accounts for TDR (Detail) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2017 | Mar. 31, 2016
Financing Receivable, Modifications [Line Items] |  |
Modified Loans | $ 215 | $ 368
Charge-Offs | 106 | 102
Payment-Default | 54 | 73
Private Education Loans - Traditional [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Modified Loans | 199 | 341
Charge-Offs | 86 | 80
Payment-Default | 47 | 62
Private Education Loans - Non-Traditional [Member] |  |
Financing Receivable, Modifications [Line Items] |  |
Modified Loans | 16 | 27
Charge-Offs | 20 | 22
Payment-Default | $ 7 | $ 11

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- Definition Pre-modification amount of investment in financing receivables modified by troubled debt restructurings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953676-111524 + Details
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- Definition Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 34 -URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953682-111524 + Details
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- Definition Reflects the amount of the write-down related to a troubled debt restructuring. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 40 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554 + Details
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