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Borrowings - Short Term Borrowings (Details) - USD ($) |  | 12 Months Ended |  |
--- | --- | --- | --- | ---
Feb. 20, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Feb. 17, 2021 | Feb. 19, 2020
Short-term Debt [Line Items] |  |  |  |  |
Short-Term |  | $ 0 | $ 289,230,000 |  |
Maximum outstanding at any month end |  | 289,230,000 | 297,800,000 |  |
Borrowing limit increase |  | 2,000,000,000 |  |  |
Secured Borrowing Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Short-Term |  | $ 0 | $ 289,230,000 |  |
Contractual maturity related to ABCP facility |  | 2 years |  |  |
Weighted Average Interest Rate |  | 0.00% | 1.74% |  |
Average Balance |  | $ 45,820,000 | $ 102,639,000 |  |
Weighted Average Interest Rate |  | 24.99% | 4.91% |  |
Commercial Paper | Secured Borrowing Facility |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Private education loan funding | $ 750,000,000 |  |  |  | $ 2,000,000,000
Ownership interest percentage | 100.00% |  |  |  |
Short-Term |  | $ 0 | $ 289,000,000 |  |
Commercial Paper | Secured Borrowing Facility | Subsequent Event |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |
Private education loan funding |  |  |  | $ 2,000,000,000 |

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