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Allowance for Credit Losses - Allowance and Recorded Investments in Loans (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Allowance for Credit Losses |  |  |
Beginning Balance | $ 1,165,335 | $ 1,361,723 | $ 441,912
Transfer from unfunded commitment liability | 344,310 | 301,655 | 320,808
Provision for current period | 413,535 | (232,708) | 190,898
Loan sale reduction to provision | (174,231) | (66,460) | (204,709)
Loans transferred to held-for-sale | 2,372 | 1,887 | 205,669
Total provisions | 236,932 | (297,281) | (219,480)
Net charge-offs |  |  |
Charge-offs | (431,244) | (230,268) | (245,043)
Recoveries | 41,742 | 29,506 | 29,007
Net charge-offs | (389,502) | (200,762) | (216,036)
Loan sales |  |  | (108,534)
Ending Balance | 1,357,075 | 1,165,335 | 1,361,723
Allowance [Abstract] |  |  |
Ending balance: individually evaluated for impairment |  | 47,712 | 104,265
Ending balance: collectively evaluated for impairment | 1,357,075 | 1,117,623 | 1,257,458
Loans [Abstract] |  |  |
Ending balance: individually evaluated for impairment |  | 1,057,665 | 1,274,590
Ending balance: collectively evaluated for impairment | 20,912,738 | 20,379,428 | 19,204,578
Accrued interest to be capitalized |  |  |
Ending balance: individually evaluated for impairment |  | 0 | 0
Ending balance: collectively evaluated for impairment | 936,837 | 947,391 | 973,201
Private Education Loan provision for credit losses, other impacts | 909 | 1,144 | (691)
Provisions for credit losses reported in consolidated statements of income | 633,453 | (32,957) | 93,133
Adjustments |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance |  | 1,143,053 |
Net charge-offs |  |  |
Ending Balance |  |  | 1,143,053
Remaining Adjusted Transition Amounts to be Phased-In |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance |  |  | 1,584,965
FFELP Loans |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance | 4,077 | 4,378 | 1,633
Transfer from unfunded commitment liability | 0 | 0 | 0
Provision for current period | (20) | 20 | 412
Loan sale reduction to provision | 0 | 0 | 0
Loans transferred to held-for-sale | 0 | 0 | 0
Total provisions | (20) | 20 | 412
Net charge-offs |  |  |
Charge-offs | (613) | (321) | (519)
Recoveries | 0 | 0 | 0
Net charge-offs | (613) | (321) | (519)
Loan sales |  |  | 0
Ending Balance | 3,444 | 4,077 | 4,378
Allowance [Abstract] |  |  |
Ending balance: individually evaluated for impairment |  | 0 | 0
Ending balance: collectively evaluated for impairment | 3,444 | 4,077 | 4,378
Loans [Abstract] |  |  |
Ending balance: individually evaluated for impairment |  | 0 | 0
Ending balance: collectively evaluated for impairment | 609,050 | 695,216 | 737,593
Accrued interest to be capitalized |  |  |
Ending balance: individually evaluated for impairment |  | 0 | 0
Ending balance: collectively evaluated for impairment | $ 0 | $ 0 | $ 0
Net charge-offs as a percentage of average loans in repayment (annualized) | 0.12% | 0.06% | 0.09%
Allowance as a percentage of the ending total loan balance and accrued interest to be capitalized | 0.57% | 0.59% | 0.59%
Allowance as a percentage of the ending loans in repayment | 0.76% | 0.74% | 0.76%
Allowance coverage of net charge-offs | 5.62 | 12.70 | 8.44
Ending total loans, gross | $ 609,050 | $ 695,216 | $ 737,593
Average loans in repayment | 517,139 | 545,689 | 549,584
Ending loans in repayment | 453,915 | 553,980 | 573,361
Accrued interest to be capitalized on loans in repayment | 0 | 0 | 0
Private Education Loan provision for credit losses, other impacts | (20) | 20 | 412
FFELP Loans | Adjustments |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance |  | 2,852 |
Net charge-offs |  |  |
Ending Balance |  |  | 2,852
FFELP Loans | Remaining Adjusted Transition Amounts to be Phased-In |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance |  |  | 4,485
Private Education Loans |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance | 1,158,977 | 1,355,844 | 374,300
Transfer from unfunded commitment liability | 344,310 | 301,655 | 320,808
Provision for current period | 410,254 | (233,852) | 148,673
Loan sale reduction to provision | (174,231) | (66,460) | (161,793)
Loans transferred to held-for-sale | 0 | 1,887 | 205,669
Total provisions | 236,023 | (298,425) | (218,789)
Net charge-offs |  |  |
Charge-offs | (427,416) | (229,591) | (205,326)
Recoveries | 41,737 | 29,494 | 24,021
Net charge-offs | (385,679) | (200,097) | (181,305)
Loan sales |  |  | 0
Ending Balance | 1,353,631 | 1,158,977 | 1,355,844
Allowance [Abstract] |  |  |
Ending balance: individually evaluated for impairment |  | 47,712 | 104,265
Ending balance: collectively evaluated for impairment | 1,353,631 | 1,111,265 | 1,251,579
Loans [Abstract] |  |  |
Ending balance: individually evaluated for impairment |  | 1,057,665 | 1,274,590
Ending balance: collectively evaluated for impairment | 20,303,688 | 19,659,198 | 18,454,747
Accrued interest to be capitalized |  |  |
Ending balance: individually evaluated for impairment |  | 0 | 0
Ending balance: collectively evaluated for impairment | $ 936,837 | $ 947,391 | $ 973,201
Net charge-offs as a percentage of average loans in repayment (annualized) | 2.55% | 1.33% | 1.17%
Allowance as a percentage of the ending total loan balance and accrued interest to be capitalized | 6.37% | 5.35% | 6.55%
Allowance as a percentage of the ending loans in repayment | 8.76% | 7.32% | 9.28%
Allowance coverage of net charge-offs | 3.51 | 5.79 | 7.48
Ending total loans, gross | $ 20,303,688 | $ 20,716,863 | $ 19,729,337
Average loans in repayment | 15,103,123 | 15,019,869 | 15,518,851
Ending loans in repayment | 15,129,550 | 15,511,212 | 14,304,821
Accrued interest to be capitalized on loans in repayment | 324,384 | 312,537 | 308,655
Provisions for loan losses | 236,023 | (298,425) | (218,789)
Provisions for unfunded loan commitments | 396,521 | 264,324 | 312,613
Total Private Education Loan provisions for credit losses | 632,544 | (34,101) | 93,824
Private Education Loans | Adjustments |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance |  | 1,060,830 |
Net charge-offs |  |  |
Ending Balance |  |  | 1,060,830
Private Education Loans | Remaining Adjusted Transition Amounts to be Phased-In |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance |  |  | 1,435,130
Personal Loans |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance |  | 0 | 65,877
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)
Net charge-offs |  |  |
Charge-offs |  |  | (39,079)
Recoveries |  |  | 4,984
Net charge-offs |  |  | (34,095)
Loan sales |  |  | (108,534)
Ending Balance |  |  | 0
Allowance [Abstract] |  |  |
Ending balance: individually evaluated for impairment |  |  | 0
Ending balance: collectively evaluated for impairment |  |  | 0
Loans [Abstract] |  |  |
Ending balance: individually evaluated for impairment |  |  | 0
Ending balance: collectively evaluated for impairment |  |  | 0
Accrued interest to be capitalized |  |  |
Ending balance: individually evaluated for impairment |  |  | 0
Ending balance: collectively evaluated for impairment |  |  | $ 0
Net charge-offs as a percentage of average loans in repayment (annualized) |  |  | 0.00%
Allowance as a percentage of the ending total loan balance and accrued interest to be capitalized |  |  | 0.00%
Allowance as a percentage of the ending loans in repayment |  |  | 0.00%
Allowance coverage of net charge-offs |  |  | 0
Ending total loans, gross |  |  | $ 0
Average loans in repayment |  |  | 0
Ending loans in repayment |  |  | 0
Accrued interest to be capitalized on loans in repayment |  |  | 0
Private Education Loan provision for credit losses, other impacts |  |  | (2,431)
Personal Loans | Adjustments |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance |  | 79,183 |
Net charge-offs |  |  |
Ending Balance |  |  | 79,183
Personal Loans | Remaining Adjusted Transition Amounts to be Phased-In |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance |  |  | 145,060
Credit Cards |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance | 2,281 | 1,501 | 102
Transfer from unfunded commitment liability | 0 | 0 | 0
Provision for current period | 3,301 | 1,124 | 1,328
Loan sale reduction to provision | 0 | 0 | 0
Loans transferred to held-for-sale | 2,372 | 0 | 0
Total provisions | 929 | 1,124 | 1,328
Net charge-offs |  |  |
Charge-offs | (3,215) | (356) | (119)
Recoveries | 5 | 12 | 2
Net charge-offs | (3,210) | (344) | (117)
Loan sales |  |  | 0
Ending Balance | 0 | 2,281 | 1,501
Allowance [Abstract] |  |  |
Ending balance: individually evaluated for impairment |  | 0 | 0
Ending balance: collectively evaluated for impairment | 0 | 2,281 | 1,501
Loans [Abstract] |  |  |
Ending balance: individually evaluated for impairment |  | 0 | 0
Ending balance: collectively evaluated for impairment | 0 | 25,014 | 12,238
Accrued interest to be capitalized |  |  |
Ending balance: individually evaluated for impairment |  | 0 | 0
Ending balance: collectively evaluated for impairment | $ 0 | $ 0 | $ 0
Net charge-offs as a percentage of average loans in repayment (annualized) | 0.00% | 2.24% | 1.26%
Allowance as a percentage of the ending total loan balance and accrued interest to be capitalized | 0.00% | 9.12% | 12.27%
Allowance as a percentage of the ending loans in repayment | 0.00% | 9.12% | 12.27%
Allowance coverage of net charge-offs | 0 | 6.63 | 12.83
Ending total loans, gross | $ 0 | $ 25,014 | $ 12,238
Average loans in repayment | 0 | 15,343 | 9,286
Ending loans in repayment | 0 | 25,014 | 12,238
Accrued interest to be capitalized on loans in repayment | 0 | 0 | 0
Private Education Loan provision for credit losses, other impacts | $ 929 | 1,124 | 1,328
Credit Cards | Adjustments |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance |  | $ 188 |
Net charge-offs |  |  |
Ending Balance |  |  | 188
Credit Cards | Remaining Adjusted Transition Amounts to be Phased-In |  |  |
Allowance for Credit Losses |  |  |
Beginning Balance |  |  | $ 290

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