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Allowance for Credit Losses - Allowance and Recorded Investments in Loans (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Dec. 31, 2020 | Dec. 31, 2019
Allowance for Credit Losses |  |  |  |  |  |
Beginning balance | $ 1,160,244 | $ 1,929,323 | $ 1,361,723 | $ 441,912 | $ 441,912 |
Transfer from unfunded commitment liability |  | 100,470 | 262,049 | 279,555 |  |
Provision for current period | (6,530) | (90,014) | (260,335) | 338,120 |  |
Loan sale reduction to provision | 0 | (42,916) | (10,335) | (204,709) |  |
Loan transfer from held-for-sale |  |  | 1,887 |  |  |
Total provisions | (6,530) | (132,930) | (268,783) | 133,411 |  |
Net charge-offs: |  |  |  |  |  |
Charge-offs | (56,225) | (60,666) | (161,569) | (178,120) |  |
Recoveries | 7,305 | 6,896 | 21,987 | 23,282 |  |
Net charge-offs | (48,920) | (53,770) | (139,582) | (154,838) |  |
Loan sales |  |  | (108,534) | (108,534) |  |
Ending Balance | 1,215,407 | 1,734,559 | 1,215,407 | 1,734,559 | 1,361,723 |
Allowance |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 69,626 | 138,663 | 69,626 | 138,663 |  |
Ending balance: collectively evaluated for impairment | 1,145,781 | 1,595,896 | 1,145,781 | 1,595,896 |  |
Loans: |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 1,148,282 | 1,495,161 | 1,148,282 | 1,495,161 |  |
Ending balance: collectively evaluated for impairment | 21,278,012 | 21,876,262 | 21,278,012 | 21,876,262 |  |
Provisions for loan losses | (6,995) | (81,710) | (269,371) | 134,374 |  |
Provisions for unfunded loan commitments | 144,972 | 129,290 | 251,135 | 276,094 |  |
Total Private Education Loan provisions for credit losses | 137,977 | 47,580 | (18,236) | 410,468 |  |
Private Education Loan provision for credit losses, other impacts | 465 | (51,220) | 588 | (963) |  |
Less: provisions for credit losses | 138,442 | (3,640) | (17,648) | 409,505 |  |
Cumulative Effect, Period Of Adoption, Adjustment |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |
Beginning balance |  |  |  | 1,584,965 | 1,584,965 |
Day 1 adjustment for the adoption of CECL |  |  |  |  |  | $ 1,143,053
Transfer from unfunded commitment liability | 110,613 |  |  |  |  |
FFELP Loans |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |
Beginning balance | 4,262 | 4,385 | 4,378 | 1,633 | 1,633 |
Transfer from unfunded commitment liability |  | 0 | 0 | 0 |  |
Provision for current period | 50 | 67 | 77 | 277 |  |
Loan sale reduction to provision | 0 | 0 | 0 | 0 |  |
Loan transfer from held-for-sale |  |  | 0 |  |  |
Total provisions | 50 | 67 | 77 | 277 |  |
Net charge-offs: |  |  |  |  |  |
Charge-offs | (106) | (89) | (249) | (399) |  |
Recoveries | 0 | 0 | 0 | 0 |  |
Net charge-offs | (106) | (89) | (249) | (399) |  |
Loan sales |  |  | 0 | 0 |  |
Ending Balance | 4,206 | 4,363 | 4,206 | 4,363 | 4,378 |
Allowance |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 0 | 0 | 0 | 0 |  |
Ending balance: collectively evaluated for impairment | 4,206 | 4,363 | 4,206 | 4,363 |  |
Loans: |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 0 | 0 | 0 | 0 |  |
Ending balance: collectively evaluated for impairment | $ 705,691 | $ 745,556 | $ 705,691 | $ 745,556 |  |
Net charge-offs as a percentage of average loans in repayment (annualized) | 0.08% | 0.07% | 0.06% | 0.10% |  |
Allowance as a percentage of the ending total loan balance | 0.60% | 0.59% | 0.60% | 0.59% |  |
Allowance as a percentage of the ending loans in repayment | 0.79% | 0.77% | 0.79% | 0.77% |  |
Allowance coverage of net charge-offs (annualized) | 9.92 | 12.26 | 12.67 | 8.20 |  |
Ending total loans, gross | $ 705,691 | $ 745,556 | $ 705,691 | $ 745,556 |  |
Average loans in repayment | 540,018 | 510,809 | 547,394 | 546,443 |  |
Ending loans in repayment | 530,476 | 564,442 | 530,476 | 564,442 |  |
Private Education Loan provision for credit losses, other impacts | 50 | 67 | 77 | 277 |  |
FFELP Loans | Cumulative Effect, Period Of Adoption, Adjustment |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |
Beginning balance |  |  |  | 4,485 | 4,485 |
Day 1 adjustment for the adoption of CECL |  |  |  |  |  | 2,852
Transfer from unfunded commitment liability | 0 |  |  |  |  |
Private Education Loans |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |
Beginning balance | 1,154,540 | 1,760,559 | 1,355,844 | 374,300 | 374,300 |
Transfer from unfunded commitment liability |  | 100,470 | 262,049 | 279,555 |  |
Provision for current period | (6,995) | (81,710) | (260,923) | 296,167 |  |
Loan sale reduction to provision | 0 | 0 | (10,335) | (161,793) |  |
Loan transfer from held-for-sale |  |  | 1,887 |  |  |
Total provisions | (6,995) | (81,710) | (269,371) | 134,374 |  |
Net charge-offs: |  |  |  |  |  |
Charge-offs | (56,000) | (55,298) | (161,039) | (138,546) |  |
Recoveries | 7,302 | 4,790 | 21,977 | 18,298 |  |
Net charge-offs | (48,698) | (50,508) | (139,062) | (120,248) |  |
Loan sales |  |  | 0 | 0 |  |
Ending Balance | 1,209,460 | 1,728,811 | 1,209,460 | 1,728,811 | 1,355,844 |
Allowance |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 69,626 | 138,663 | 69,626 | 138,663 |  |
Ending balance: collectively evaluated for impairment | 1,139,834 | 1,590,148 | 1,139,834 | 1,590,148 |  |
Loans: |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 1,148,282 | 1,495,161 | 1,148,282 | 1,495,161 |  |
Ending balance: collectively evaluated for impairment | $ 20,554,555 | $ 21,119,166 | $ 20,554,555 | $ 21,119,166 |  |
Net charge-offs as a percentage of average loans in repayment (annualized) | 1.29% | 1.33% | 1.25% | 1.05% |  |
Allowance as a percentage of the ending total loan balance | 5.57% | 7.64% | 5.57% | 7.64% |  |
Allowance as a percentage of the ending loans in repayment | 7.81% | 10.91% | 7.81% | 10.91% |  |
Allowance coverage of net charge-offs (annualized) | 6.21 | 8.56 | 6.52 | 10.78 |  |
Ending total loans, gross | $ 21,702,837 | $ 22,614,327 | $ 21,702,837 | $ 22,614,327 |  |
Average loans in repayment | 15,108,802 | 15,182,703 | 14,877,937 | 15,336,253 |  |
Ending loans in repayment | 15,490,132 | 15,853,309 | 15,490,132 | 15,853,309 |  |
Private Education Loans | Cumulative Effect, Period Of Adoption, Adjustment |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |
Beginning balance |  |  |  | 1,435,130 | 1,435,130 |
Day 1 adjustment for the adoption of CECL |  |  |  |  |  | 1,060,830
Transfer from unfunded commitment liability | 110,613 |  |  |  |  |
Personal Loans |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |
Beginning balance |  | 163,337 |  | 65,877 | 65,877 |
Transfer from unfunded commitment liability |  | 0 |  | 0 |  |
Provision for current period |  | (8,762) |  | 40,485 |  |
Loan sale reduction to provision |  | (42,916) |  | (42,916) |  |
Total provisions |  | (51,678) |  | (2,431) |  |
Net charge-offs: |  |  |  |  |  |
Charge-offs |  | (5,231) |  | (39,079) |  |
Recoveries |  | 2,106 |  | 4,984 |  |
Net charge-offs |  | (3,125) |  | (34,095) |  |
Loan sales |  |  | (108,534) | (108,534) |  |
Ending Balance |  | 0 |  | 0 |  |
Allowance |  |  |  |  |  |
Ending balance: individually evaluated for impairment |  | 0 |  | 0 |  |
Ending balance: collectively evaluated for impairment |  | 0 |  | 0 |  |
Loans: |  |  |  |  |  |
Ending balance: individually evaluated for impairment |  | 0 |  | 0 |  |
Ending balance: collectively evaluated for impairment |  | $ 0 |  | $ 0 |  |
Net charge-offs as a percentage of average loans in repayment (annualized) |  | 0.00% |  | 0.00% |  |
Allowance as a percentage of the ending total loan balance |  | 0.00% |  | 0.00% |  |
Allowance as a percentage of the ending loans in repayment |  | 0.00% |  | 0.00% |  |
Allowance coverage of net charge-offs (annualized) |  | 0 |  | 0 |  |
Ending total loans, gross |  | $ 0 |  | $ 0 |  |
Average loans in repayment |  | 0 |  | 0 |  |
Ending loans in repayment |  | 0 |  | 0 |  |
Private Education Loan provision for credit losses, other impacts |  | (51,678) |  | (2,431) |  |
Personal Loans | Cumulative Effect, Period Of Adoption, Adjustment |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |
Beginning balance |  |  |  | 145,060 | 145,060 |
Day 1 adjustment for the adoption of CECL |  |  |  |  |  | 79,183
Credit Cards |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |
Beginning balance | 1,442 | 1,042 | 1,501 | 102 | 102 |
Transfer from unfunded commitment liability |  | 0 | 0 | 0 |  |
Provision for current period | 415 | 391 | 511 | 1,191 |  |
Loan sale reduction to provision | 0 | 0 | 0 | 0 |  |
Loan transfer from held-for-sale |  |  | 0 |  |  |
Total provisions | 415 | 391 | 511 | 1,191 |  |
Net charge-offs: |  |  |  |  |  |
Charge-offs | (119) | (48) | (281) | (96) |  |
Recoveries | 3 | 0 | 10 | 0 |  |
Net charge-offs | (116) | (48) | (271) | (96) |  |
Loan sales |  |  | 0 | 0 |  |
Ending Balance | 1,741 | 1,385 | 1,741 | 1,385 | 1,501 |
Allowance |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 0 | 0 | 0 | 0 |  |
Ending balance: collectively evaluated for impairment | 1,741 | 1,385 | 1,741 | 1,385 |  |
Loans: |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 0 | 0 | 0 | 0 |  |
Ending balance: collectively evaluated for impairment | $ 17,766 | $ 11,540 | $ 17,766 | $ 11,540 |  |
Net charge-offs as a percentage of average loans in repayment (annualized) | 3.07% | 1.73% | 2.75% | 1.51% |  |
Allowance as a percentage of the ending total loan balance | 9.80% | 12.00% | 9.80% | 12.00% |  |
Allowance as a percentage of the ending loans in repayment | 9.80% | 12.00% | 9.80% | 12.00% |  |
Allowance coverage of net charge-offs (annualized) | 3.75 | 7.21 | 4.82 | 10.82 |  |
Ending total loans, gross | $ 17,766 | $ 11,540 | $ 17,766 | $ 11,540 |  |
Average loans in repayment | 15,098 | 11,103 | 13,136 | 8,499 |  |
Ending loans in repayment | 17,766 | 11,540 | 17,766 | 11,540 |  |
Private Education Loan provision for credit losses, other impacts | 415 | $ 391 | $ 511 | 1,191 |  |
Credit Cards | Cumulative Effect, Period Of Adoption, Adjustment |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |
Beginning balance |  |  |  | $ 290 | $ 290 |
Day 1 adjustment for the adoption of CECL |  |  |  |  |  | $ 188
Transfer from unfunded commitment liability | $ 0 |  |  |  |  |

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