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Allowance for Loan Losses - Allowance for Credit Losses and Recorded Investments in Loans (Parenthetical) (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Sale of private education loan | $ 30 |  | $ 1,600 |
End of period expected recoveries | 434 | $ 549 | 434 | $ 549
Change in balance during period | (20) | (22) | (45) | (39)
Private Education Loans [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning of period expected recoveries | 454 | 571 | 479 | 588
Expected future recoveries of current period defaults | 5 | 9 | 10 | 22
Recoveries | (22) | (28) | (47) | (57)
Charge-offs | (3) | (3) | (8) | (4)
End of period expected recoveries | 434 | 549 | 434 | 549
Change in balance during period | $ (20) | $ (22) | $ (45) | $ (39)

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- Definition Expected future recoveries on charged-off loans. + References No definition available. + Details
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- Definition Represents the difference between the loan balance and the company's estimate of the amount to be collected in the future. + References No definition available. + Details
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- Definition Sale of private education loan. + 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 increase in allowance for credit loss on financing receivable from recovery. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524 + Details
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- Definition Amount of writeoff of financing receivable, charged against allowance for credit loss. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 79 -URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448 + Details
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- Definition Amount of expense (reversal of expense) for expected credit loss on financing receivable, from change in present value of expected cash flows. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919246-210447 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82919204-210446 + Details
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- Details
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