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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, 2025 | Jun. 30, 2024 | Jun. 30, 2025 | Jun. 30, 2024
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Adjustment resulting from the change in the charge-off rate | $ (1) | $ 0 | $ (2) | $ 0
Expected future recoveries of current period defaults | 13 | 10 | 23 | 21
Charge-offs (as a result of lower recovery expectations) | (100) | (87) | (187) | (207)
Change in balance during period | (2) | (6) | (8) | (15)
Private Education Loans [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Adjustment resulting from the change in the charge-off rate | (1) | 0 | (2) | 0
Expected future recoveries of current period defaults | 13 | 10 | 23 | 21
Charge-offs (as a result of lower recovery expectations) | (92) | (77) | (173) | (187)
Change in balance during period | (2) | (6) | (8) | (15)
Private Education Loans [Member] | Loans Receivable For Previously Fully Charged Off Loans [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Beginning of period expected future recoveries on previously fully charged-off loans | 174 | 217 | 179 | 226
Expected future recoveries of current period defaults | 13 | 10 | 23 | 21
Recoveries (cash collected) | (11) | (10) | (21) | (21)
Charge-offs (as a result of lower recovery expectations) | (4) | (6) | (10) | (15)
End of period expected future recoveries on previously fully charged-off loans | 172 | 211 | 172 | 211
Change in balance during period | $ (2) | $ (6) | $ (8) | $ (15)

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- Definition Expected future recoveries on previously fully charged-off loans. + References No definition available. + Details
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- Definition Financing receivable decrease in expected future recoveries on previous fully 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 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 Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 310 -SubTopic 20 -Name Accounting Standards Codification -Section 40 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481628/310-20-40-7 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481990/310-10-45-2 + Details
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