Borrowings - Secured Financing (Details) - USD ($)	1 Months Ended
	Nov. 30, 2021	Aug. 31, 2021	May 31, 2021	Aug. 31, 2020	Feb. 29, 2020	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total Issued						$ 1,592,000,000	$ 1,343,000,000
Total loans and accrued interest amount securitized at inception						1,656,263,000	$ 1,463,230,000
2020-A
Debt Instrument [Line Items]
Total Issued					$ 636,000,000
Basis spread on variable rate					0.88%
Weighted Average Life (in years)					4 years 2 months 4 days
2020-B
Debt Instrument [Line Items]
Total Issued				$ 707,000,000
Basis spread on variable rate				1.30%
Weighted Average Life (in years)				4 years 1 month 20 days
2021-B
Debt Instrument [Line Items]
Total Issued			$ 531,000,000
Basis spread on variable rate			0.77%
Weighted Average Life (in years)			4 years 3 months 3 days
Loans Pledged as Collateral						496,000,000
Principal amount of collateral						467,000,000
Capitalized interest						29,000,000
2021-D
Debt Instrument [Line Items]
Total Issued		$ 527,000,000
Basis spread on variable rate		0.69%
Weighted Average Life (in years)		4 years 2 months 19 days
Loans Pledged as Collateral						515,000,000
Principal amount of collateral						485,000,000
Capitalized interest						30,000,000
2021-E
Debt Instrument [Line Items]
Total Issued	$ 534,000,000
Basis spread on variable rate	0.69%
Weighted Average Life (in years)	4 years 1 month 24 days
Loans Pledged as Collateral						533,000,000
Principal amount of collateral						502,000,000
Capitalized interest						31,000,000
Private Education Loan term securitizations
Debt Instrument [Line Items]
Loans Pledged as Collateral						1,110,000,000
Principal amount of collateral						1,050,000,000.00
Capitalized interest						$ 62,000,000