Borrowings - Secured Financing (Details) - USD ($)	1 Months Ended
	May 31, 2024	Aug. 31, 2023	Mar. 31, 2023	Jun. 30, 2024	Dec. 31, 2023
Securities Financing Transaction [Line Items]
Total Issued				$ 668,000,000	$ 1,147,000,000
Total loans and accrued interest amount securitized at inception				733,644,000	$ 1,292,507,000
2023-A
Securities Financing Transaction [Line Items]
Total Issued			$ 579,000,000
Weighted Average Cost of Funds (as a percent)			1.53%
Weighted Average Life (in years)			5 years 21 days
2023-C
Securities Financing Transaction [Line Items]
Total Issued		$ 568,000,000
Weighted Average Cost of Funds (as a percent)		1.69%
Weighted Average Life (in years)		4 years 11 months 4 days
Principal amount of collateral				670,000,000
Capitalized interest				57,000,000
2024-C
Securities Financing Transaction [Line Items]
Total Issued	$ 668,000,000
Weighted Average Cost of Funds (as a percent)	1.19%
Weighted Average Life (in years)	5 years 4 months 9 days
Private Education Loans Securitized In 2023
Securities Financing Transaction [Line Items]
Loans				1,140,000,000
Principal amount of collateral				1,060,000,000.00
Capitalized interest				84,000,000
Private Education Loans Securitized In 2024
Securities Financing Transaction [Line Items]
Loans				727,000,000
Principal amount of collateral				670,000,000
Capitalized interest				$ 57,000,000