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Allowance for Credit Losses - Allowance and Recorded Investments in Loans (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2021 | Sep. 30, 2021 | Jun. 30, 2021 | Mar. 31, 2021 | Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Allowance for Credit Losses |  |  |  |  |  |  |  |  |  |  |
Beginning balance |  |  |  | $ 1,361,723 |  |  |  | $ 441,912 | $ 1,361,723 | $ 441,912 | $ 341,121
Transfer from unfunded commitment liability |  |  |  |  |  |  |  |  | 301,655 | 320,808 |
Provision for current period |  |  |  |  |  |  |  |  | (232,708) | 190,898 |
Loan sale reduction to provision |  |  |  |  |  |  |  |  | (66,460) | (204,709) |
Loans transferred to held-for-sale |  |  |  |  |  |  |  |  | 1,887 | (205,669) |
Total provisions |  |  |  |  |  |  |  |  | (297,281) | (219,480) | 353,934
Net charge-offs: |  |  |  |  |  |  |  |  |  |  |
Charge-offs |  |  |  |  |  |  |  |  | (230,268) | (245,043) | (284,114)
Recoveries |  |  |  |  |  |  |  |  | 29,506 | 29,007 | 30,971
Net charge-offs |  |  |  |  |  |  |  |  | (200,762) | (216,036) | (253,143)
Loan sales |  |  |  |  |  |  |  |  |  | (108,534) |
Ending balance | $ 1,165,335 |  |  |  | $ 1,361,723 |  |  |  | 1,165,335 | 1,361,723 | 441,912
Allowance: |  |  |  |  |  |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 47,712 |  |  |  | 104,265 |  |  |  | 47,712 | 104,265 | 186,697
Ending balance: collectively evaluated for impairment | 1,117,623 |  |  |  | 1,257,458 |  |  |  | 1,117,623 | 1,257,458 | 255,215
Loans: |  |  |  |  |  |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 1,057,665 |  |  |  | 1,274,590 |  |  |  | 1,057,665 | 1,274,590 | 1,581,966
Ending balance: collectively evaluated for impairment | 20,379,428 |  |  |  | 19,204,578 |  |  |  | 20,379,428 | 19,204,578 | 23,443,822
Provisions for unfunded loan commitments |  |  |  |  |  |  |  |  | 232,822 | 311,659 | 5,937
Less: provisions for credit losses | (15,309) | $ 138,442 | $ 69,677 | (225,767) | (316,372) | $ (3,640) | $ 351,887 | 61,258 | (32,957) | 93,133 | 354,249
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
Net charge-offs: |  |  |  |  |  |  |  |  |  |  |
Ending balance |  |  |  |  |  |  |  |  |  |  | 1,584,965
Private Education Loans |  |  |  |  |  |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |  |  |  |  |  |
Beginning balance |  |  |  | 1,355,844 |  |  |  | 374,300 | 1,355,844 | 374,300 | 277,943
Transfer from unfunded commitment liability |  |  |  |  |  |  |  |  | 301,655 | 320,808 |
Provision for current period |  |  |  |  |  |  |  |  | (233,852) | 148,673 |
Loan sale reduction to provision |  |  |  |  |  |  |  |  | (66,460) | (161,793) |
Loans transferred to held-for-sale |  |  |  |  |  |  |  |  | 1,887 | (205,669) |
Total provisions |  |  |  |  |  |  |  |  | (298,425) | (218,789) | 279,570
Net charge-offs: |  |  |  |  |  |  |  |  |  |  |
Charge-offs |  |  |  |  |  |  |  |  | (229,591) | (205,326) | (208,978)
Recoveries |  |  |  |  |  |  |  |  | 29,494 | 24,021 | 25,765
Net charge-offs |  |  |  |  |  |  |  |  | (200,097) | (181,305) | (183,213)
Loan sales |  |  |  |  |  |  |  |  |  | 0 |
Ending balance | 1,158,977 |  |  |  | 1,355,844 |  |  |  | 1,158,977 | 1,355,844 | 374,300
Allowance: |  |  |  |  |  |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 47,712 |  |  |  | 104,265 |  |  |  | 47,712 | 104,265 | 186,697
Ending balance: collectively evaluated for impairment | 1,111,265 |  |  |  | 1,251,579 |  |  |  | 1,111,265 | 1,251,579 | 187,603
Loans: |  |  |  |  |  |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 1,057,665 |  |  |  | 1,274,590 |  |  |  | 1,057,665 | 1,274,590 | 1,581,966
Ending balance: collectively evaluated for impairment | 19,659,198 |  |  |  | 18,454,747 |  |  |  | $ 19,659,198 | $ 18,454,747 | $ 21,607,625
Net charge-offs as a percentage of average loans in repayment (annualized) |  |  |  |  |  |  |  |  | 1.33% | 1.17% | 1.17%
Allowance as a percentage of the ending total loan balance |  |  |  |  |  |  |  |  | 5.59% | 6.87% | 1.61%
Allowance as a percentage of the ending loans in repayment |  |  |  |  |  |  |  |  | 7.47% | 9.48% | 2.23%
Allowance coverage of net charge-offs (annualized) |  |  |  |  |  |  |  |  | 5.79 | 7.48 | 2.04
Ending total loans, gross | 20,716,863 |  |  |  | 19,729,337 |  |  |  | $ 20,716,863 | $ 19,729,337 | $ 23,189,591
Average loans in repayment |  |  |  |  |  |  |  |  | 15,019,869 | 15,518,851 | 15,605,927
Ending loans in repayment | 15,511,212 |  |  |  | 14,304,821 |  |  |  | 15,511,212 | 14,304,821 | 16,787,670
Provisions for unfunded loan commitments |  |  |  |  |  |  |  |  | 264,324 | 312,613 |
Less: provisions for credit losses |  |  |  |  |  |  |  |  | (34,101) | 93,824 |
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
Net charge-offs: |  |  |  |  |  |  |  |  |  |  |
Ending balance |  |  |  |  |  |  |  |  |  |  | 1,435,130
Other Industries, Excluding Private Education Loans |  |  |  |  |  |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |  |  |  |  |  |
Total provisions |  |  |  |  |  |  |  |  | 1,144 | (691) |
FFELP Loans |  |  |  |  |  |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |  |  |  |  |  |
Beginning balance |  |  |  | 4,378 |  |  |  | 1,633 | 4,378 | 1,633 | 977
Transfer from unfunded commitment liability |  |  |  |  |  |  |  |  | 0 | 0 |
Provision for current period |  |  |  |  |  |  |  |  | 20 | 412 |
Loan sale reduction to provision |  |  |  |  |  |  |  |  | 0 | 0 |
Loans transferred to held-for-sale |  |  |  |  |  |  |  |  | 0 | 0 |
Total provisions |  |  |  |  |  |  |  |  | 20 | 412 | 1,478
Net charge-offs: |  |  |  |  |  |  |  |  |  |  |
Charge-offs |  |  |  |  |  |  |  |  | (321) | (519) | (822)
Recoveries |  |  |  |  |  |  |  |  | 0 | 0 | 0
Net charge-offs |  |  |  |  |  |  |  |  | (321) | (519) | (822)
Loan sales |  |  |  |  |  |  |  |  |  | 0 |
Ending balance | 4,077 |  |  |  | 4,378 |  |  |  | 4,077 | 4,378 | 1,633
Allowance: |  |  |  |  |  |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 0 |  |  |  | 0 |  |  |  | 0 | 0 | 0
Ending balance: collectively evaluated for impairment | 4,077 |  |  |  | 4,378 |  |  |  | 4,077 | 4,378 | 1,633
Loans: |  |  |  |  |  |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 0 |  |  |  | 0 |  |  |  | 0 | 0 | 0
Ending balance: collectively evaluated for impairment | 695,216 |  |  |  | 737,593 |  |  |  | $ 695,216 | $ 737,593 | $ 783,306
Net charge-offs as a percentage of average loans in repayment (annualized) |  |  |  |  |  |  |  |  | 0.06% | 0.09% | 0.13%
Allowance as a percentage of the ending total loan balance |  |  |  |  |  |  |  |  | 0.59% | 0.59% | 0.21%
Allowance as a percentage of the ending loans in repayment |  |  |  |  |  |  |  |  | 0.74% | 0.76% | 0.26%
Allowance coverage of net charge-offs (annualized) |  |  |  |  |  |  |  |  | 12.70 | 8.44 | 1.99
Ending total loans, gross | 695,216 |  |  |  | 737,593 |  |  |  | $ 695,216 | $ 737,593 | $ 783,306
Average loans in repayment |  |  |  |  |  |  |  |  | 545,689 | 549,584 | 631,029
Ending loans in repayment | 553,980 |  |  |  | 573,361 |  |  |  | 553,980 | 573,361 | 617,646
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
Net charge-offs: |  |  |  |  |  |  |  |  |  |  |
Ending balance |  |  |  |  |  |  |  |  |  |  | 4,485
Credit Cards |  |  |  |  |  |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |  |  |  |  |  |
Beginning balance |  |  |  | 1,501 |  |  |  | 102 | 1,501 | 102 | 0
Transfer from unfunded commitment liability |  |  |  |  |  |  |  |  | 0 | 0 |
Provision for current period |  |  |  |  |  |  |  |  | 1,124 | 1,328 |
Loan sale reduction to provision |  |  |  |  |  |  |  |  | 0 | 0 |
Loans transferred to held-for-sale |  |  |  |  |  |  |  |  | 0 | 0 |
Total provisions |  |  |  |  |  |  |  |  | 1,124 | 1,328 | 103
Net charge-offs: |  |  |  |  |  |  |  |  |  |  |
Charge-offs |  |  |  |  |  |  |  |  | (356) | (119) | (1)
Recoveries |  |  |  |  |  |  |  |  | 12 | 2 | 0
Net charge-offs |  |  |  |  |  |  |  |  | (344) | (117) | (1)
Loan sales |  |  |  |  |  |  |  |  |  | 0 |
Ending balance | 2,281 |  |  |  | 1,501 |  |  |  | 2,281 | 1,501 | 102
Allowance: |  |  |  |  |  |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 0 |  |  |  | 0 |  |  |  | 0 | 0 | 0
Ending balance: collectively evaluated for impairment | 2,281 |  |  |  | 1,501 |  |  |  | 2,281 | 1,501 | 102
Loans: |  |  |  |  |  |  |  |  |  |  |
Ending balance: individually evaluated for impairment | 0 |  |  |  | 0 |  |  |  | 0 | 0 | 0
Ending balance: collectively evaluated for impairment | 25,014 |  |  |  | 12,238 |  |  |  | $ 25,014 | $ 12,238 | $ 3,884
Net charge-offs as a percentage of average loans in repayment (annualized) |  |  |  |  |  |  |  |  | 2.24% | 1.26% | 0.13%
Allowance as a percentage of the ending total loan balance |  |  |  |  |  |  |  |  | 9.12% | 12.27% | 2.63%
Allowance as a percentage of the ending loans in repayment |  |  |  |  |  |  |  |  | 9.12% | 12.27% | 2.63%
Allowance coverage of net charge-offs (annualized) |  |  |  |  |  |  |  |  | 6.63 | 12.83 | 102.00
Ending total loans, gross | 25,014 |  |  |  | 12,238 |  |  |  | $ 25,014 | $ 12,238 | $ 3,884
Average loans in repayment |  |  |  |  |  |  |  |  | 15,343 | 9,286 | 786
Ending loans in repayment | $ 25,014 |  |  |  | 12,238 |  |  |  | 25,014 | 12,238 | 3,884
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
Net charge-offs: |  |  |  |  |  |  |  |  |  |  |
Ending balance |  |  |  |  |  |  |  |  |  |  | 290
Personal Loans |  |  |  |  |  |  |  |  |  |  |
Allowance for Credit Losses |  |  |  |  |  |  |  |  |  |  |
Beginning balance |  |  |  | $ 0 |  |  |  | 65,877 | $ 0 | 65,877 | 62,201
Transfer from unfunded commitment liability |  |  |  |  |  |  |  |  |  | 0 |
Provision for current period |  |  |  |  |  |  |  |  |  | 40,485 |
Loan sale reduction to provision |  |  |  |  |  |  |  |  |  | (42,916) |
Loans transferred to held-for-sale |  |  |  |  |  |  |  |  |  | 0 |
Total provisions |  |  |  |  |  |  |  |  |  | (2,431) | 72,783
Net charge-offs: |  |  |  |  |  |  |  |  |  |  |
Charge-offs |  |  |  |  |  |  |  |  |  | (39,079) | (74,313)
Recoveries |  |  |  |  |  |  |  |  |  | 4,984 | 5,206
Net charge-offs |  |  |  |  |  |  |  |  |  | (34,095) | (69,107)
Loan sales |  |  |  |  |  |  |  |  |  | (108,534) |
Ending balance |  |  |  |  | 0 |  |  |  |  | 0 | 65,877
Allowance: |  |  |  |  |  |  |  |  |  |  |
Ending balance: individually evaluated for impairment |  |  |  |  | 0 |  |  |  |  | 0 | 0
Ending balance: collectively evaluated for impairment |  |  |  |  | 0 |  |  |  |  | 0 | 65,877
Loans: |  |  |  |  |  |  |  |  |  |  |
Ending balance: individually evaluated for impairment |  |  |  |  | 0 |  |  |  |  | 0 | 0
Ending balance: collectively evaluated for impairment |  |  |  |  | 0 |  |  |  |  | $ 0 | $ 1,049,007
Net charge-offs as a percentage of average loans in repayment (annualized) |  |  |  |  |  |  |  |  |  | 0.00% | 6.07%
Allowance as a percentage of the ending total loan balance |  |  |  |  |  |  |  |  |  | 0.00% | 6.28%
Allowance as a percentage of the ending loans in repayment |  |  |  |  |  |  |  |  |  | 0.00% | 6.28%
Allowance coverage of net charge-offs (annualized) |  |  |  |  |  |  |  |  |  | 0 | 0.95
Ending total loans, gross |  |  |  |  | 0 |  |  |  |  | $ 0 | $ 1,049,007
Average loans in repayment |  |  |  |  |  |  |  |  |  | 0 | 1,138,887
Ending loans in repayment |  |  |  |  | $ 0 |  |  |  |  | 0 | 1,049,007
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
Net charge-offs: |  |  |  |  |  |  |  |  |  |  |
Ending balance |  |  |  |  |  |  |  |  |  |  | $ 145,060

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