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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 | 9 Months Ended
--- | --- | ---
Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2022 | Sep. 30, 2021
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Adjustment resulting from the change in charge-off rate | $ 30 | $ 16 | $ 30 | $ 16
Expected future recoveries of current period defaults | 19 | 6 | 43 | 16
Change in balance during period | (32) | (37) | (49) | (82)
Sale of private education loan |  |  |  | 1,600
Private Education Loans [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Adjustment resulting from the change in charge-off rate | 30 | 16 | 30 | 16
Beginning of period expected future recoveries on previously fully charged-off loans | 312 | 434 | 329 | 479
Expected future recoveries of current period defaults | 19 | 6 | 43 | 16
Recoveries (cash collected) | (14) | (22) | (43) | (69)
Charge-offs (as a result of lower recovery expectations) | (37) | (21) | (49) | (29)
End of period expected future recoveries on previously fully charged-off loans | 280 | 397 | 280 | 397
Change in balance during period | (32) | (37) | $ (49) | $ (82)
Private Education Loans [Member] | Loans Receivable For Previously Fully Charged Off Loans [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Adjustment resulting from the change in charge-off rate | $ 30 | $ 16 |  |
Private Education Loans [Member] | Minimum [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Net charge off rate on defaulted loans | 81.70% | 81.40% |  |
Private Education Loans [Member] | MaximumMember |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Net charge off rate on defaulted loans | 81.90% | 81.70% |  |

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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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