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Allowance for Loan Losses - Private Education Loan Portfolio Stratified by Key Credit Quality Indicators (Detail) - USD ($) $ in Millions | Sep. 30, 2022 | Jun. 30, 2022 | Dec. 31, 2021 | Sep. 30, 2021 | Jun. 30, 2021 | Dec. 31, 2020
--- | --- | --- | --- | --- | --- | ---
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Loan allowance for losses | $ (1,085) | $ (1,166) | $ (1,271) | $ (1,249) | $ (1,253) | $ (1,377)
Private Education Loans [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | 20,003 |  |  | 20,998 |  |
Loan allowance for losses | (852) | $ (921) | (1,009) | (980) | $ (976) | $ (1,089)
Loans, net | 19,151 |  | $ 20,171 | 20,018 |  |
FICO Scores [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | 1,520 |  |  | 4,077 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 4,772 |  |  | 2,238 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 1,612 |  |  | 2,097 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 1,539 |  |  | 782 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 576 |  |  | 241 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 9,984 |  |  | 11,563 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 20,003 |  |  | $ 20,998 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 100.00% |  |  | 100.00% |  |
FICO Scores [Member] | 640 and Above [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1,503 |  |  | $ 4,049 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 4,708 |  |  | 2,228 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 1,593 |  |  | 2,064 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 1,502 |  |  | 762 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 556 |  |  | 233 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 8,485 |  |  | 10,021 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 18,347 |  |  | $ 19,357 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 92.00% |  |  | 92.00% |  |
FICO Scores [Member] | Below 640 [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 17 |  |  | $ 28 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 64 |  |  | 10 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 19 |  |  | 33 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 37 |  |  | 20 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 20 |  |  | 8 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 1,499 |  |  | 1,542 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 1,656 |  |  | $ 1,641 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 8.00% |  |  | 8.00% |  |
Loan Status [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1,520 |  |  | $ 4,077 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 4,772 |  |  | 2,238 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 1,612 |  |  | 2,097 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 1,539 |  |  | 782 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 576 |  |  | 241 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 9,984 |  |  | 11,563 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 20,003 |  |  | $ 20,998 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 100.00% |  |  | 100.00% |  |
Loan Status [Member] | School/Grace/Deferment [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 31 |  |  | $ 32 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 88 |  |  | 34 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 28 |  |  | 45 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 34 |  |  | 19 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 13 |  |  | 8 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 525 |  |  | 1,065 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 719 |  |  | $ 1,203 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 4.00% |  |  | 6.00% |  |
Loan Status [Member] | Current/90 Days or Less Delinquent [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1,488 |  |  | $ 4,044 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 4,678 |  |  | 2,203 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 1,582 |  |  | 2,049 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 1,499 |  |  | 762 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 560 |  |  | 232 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 9,083 |  |  | 10,289 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 18,890 |  |  | $ 19,579 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 94.00% |  |  | 93.00% |  |
Loan Status [Member] | Greater than 90 days Delinquent [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1 |  |  | $ 1 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 6 |  |  | 1 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 2 |  |  | 3 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 6 |  |  | 1 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 3 |  |  | 1 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 376 |  |  | 209 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 394 |  |  | $ 216 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 2.00% |  |  | 1.00% |  |
School Type [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1,520 |  |  | $ 4,077 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 4,772 |  |  | 2,238 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 1,612 |  |  | 2,097 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 1,539 |  |  | 782 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 576 |  |  | 241 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 9,984 |  |  | 11,563 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 20,003 |  |  | $ 20,998 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 100.00% |  |  | 100.00% |  |
School Type [Member] | Not For Profit [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1,427 |  |  | $ 3,850 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 4,496 |  |  | 2,137 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 1,541 |  |  | 1,957 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 1,434 |  |  | 721 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 529 |  |  | 231 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 8,338 |  |  | 9,607 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 17,765 |  |  | $ 18,503 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 89.00% |  |  | 88.00% |  |
School Type [Member] | For Profit [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 93 |  |  | $ 227 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 276 |  |  | 101 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 71 |  |  | 140 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 105 |  |  | 61 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 47 |  |  | 10 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 1,646 |  |  | 1,956 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 2,238 |  |  | $ 2,495 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 11.00% |  |  | 12.00% |  |
Cosigners [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1,520 |  |  | $ 4,077 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 4,772 |  |  | 2,238 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 1,612 |  |  | 2,097 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 1,539 |  |  | 782 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 576 |  |  | 241 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 9,984 |  |  | 11,563 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 20,003 |  |  | $ 20,998 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 100.00% |  |  | 100.00% |  |
Cosigners [Member] | With Cosigner [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 24 |  |  | $ 12 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 109 |  |  | 34 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 28 |  |  | 13 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 11 |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five |  |  |  | 37 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 6,425 |  |  | 7,560 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 6,597 |  |  | $ 7,656 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 33.00% |  |  | 36.00% |  |
Cosigners [Member] | Without Cosigner [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1,496 |  |  | $ 4,065 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 4,663 |  |  | 2,204 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 1,584 |  |  | 2,084 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 1,528 |  |  | 782 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 576 |  |  | 204 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 3,559 |  |  | 4,003 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 13,406 |  |  | $ 13,342 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 67.00% |  |  | 64.00% |  |
Private Education Loans Troubled Debt Restructuring Status |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1,520 |  |  | $ 4,077 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 4,772 |  |  | 2,238 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 1,612 |  |  | 2,097 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 1,539 |  |  | 782 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 576 |  |  | 241 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 9,984 |  |  | 11,563 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 20,003 |  |  | $ 20,998 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 100.00% |  |  | 100.00% |  |
Private Education Loans Troubled Debt Restructuring Status | Private Education Loans - TDRs [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 6 |  |  | $ 1 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 48 |  |  | 5 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 28 |  |  | 26 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 62 |  |  | 27 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 35 |  |  | 30 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 6,617 |  |  | 7,323 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 6,796 |  |  | $ 7,412 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 34.00% |  |  | 35.00% |  |
Private Education Loans Troubled Debt Restructuring Status | Private Education Loans - Non-TDRs [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1,514 |  |  | $ 4,076 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 4,724 |  |  | 2,233 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 1,584 |  |  | 2,071 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 1,477 |  |  | 755 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 541 |  |  | 211 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 3,367 |  |  | 4,240 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 13,207 |  |  | $ 13,586 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 66.00% |  |  | 65.00% |  |
Seasoning [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1,520 |  |  | $ 4,077 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 4,772 |  |  | 2,238 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 1,612 |  |  | 2,097 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 1,539 |  |  | 782 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 576 |  |  | 241 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 9,984 |  |  | 11,563 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 20,003 |  |  | $ 20,998 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 100.00% |  |  | 100.00% |  |
Seasoning [Member] | 1-12 Payments [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 1,499 |  |  | $ 4,058 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 2,186 |  |  | 1,017 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 14 |  |  | 37 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 10 |  |  | 5 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 2 |  |  | 1 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 95 |  |  | 142 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 3,806 |  |  | $ 5,260 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 19.00% |  |  | 25.00% |  |
Seasoning [Member] | 13-24 Payments [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | $ 2,534 |  |  | $ 1,201 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 736 |  |  | 1,330 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 39 |  |  | 20 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 8 |  |  | 4 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 102 |  |  | 167 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 3,419 |  |  | $ 2,722 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 17.00% |  |  | 13.00% |  |
Seasoning [Member] | 25-36 Payments [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | $ 846 |  |  | $ 709 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 968 |  |  | 385 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 19 |  |  | 12 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 177 |  |  | 273 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 2,010 |  |  | $ 1,379 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 10.00% |  |  | 7.00% |  |
Seasoning [Member] | 37-48 Payments [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | $ 503 |  |  | $ 364 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 287 |  |  | 133 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 293 |  |  | 417 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 1,083 |  |  | $ 914 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 5.00% |  |  | 4.00% |  |
Seasoning [Member] | More than 48 Payments [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | $ 254 |  |  | $ 89 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 9,083 |  |  | 10,245 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 9,337 |  |  | $ 10,334 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 47.00% |  |  | 49.00% |  |
Seasoning [Member] | School/Grace/Deferment [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Total Private Education Loan Credit Quality Indicators by Origination Year One | $ 21 |  |  | $ 19 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Two | 52 |  |  | 20 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Three | 16 |  |  | 21 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Four | 19 |  |  | 8 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Five | 6 |  |  | 2 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year Prior | 234 |  |  | 319 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year | $ 348 |  |  | $ 389 |  |
Total Private Education Loan Credit Quality Indicators by Origination Year, Percent | 2.00% |  |  | 2.00% |  |

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