Borrowings - Long Term Borrowings Narrative (Details) - USD ($)					12 Months Ended
	Aug. 16, 2023	Mar. 15, 2023	Aug. 09, 2022	Nov. 01, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Aug. 31, 2023	Mar. 31, 2023	Aug. 31, 2022	Oct. 29, 2020
Debt Instrument [Line Items]
Total Issued					$ 1,147,000,000	$ 575,000,000
Unsecured debt issued					$ 0	$ 0	$ 492,135,000
Estimated weighted average life of student loans					5 years	5 years
Senior Unsecured Notes Due October 29, 2025 | Unsecured Debt
Debt Instrument [Line Items]
Total Issued					$ 497,000,000						$ 500,000,000
Interest rate											4.20%
Senior Unsecured Notes Due November 2, 2026 | Unsecured Debt
Debt Instrument [Line Items]
Total Issued				$ 500,000,000	495,000,000
Interest rate				3.125%
Issuance price				99.43%
2023-A
Debt Instrument [Line Items]
Total Issued									$ 579,000,000
Private education loan term accounted for as a secured financing		$ 579,000,000
Loans sold to third parties		$ 579,000,000
Ownership interest percentage on asset-backed financing		100.00%
Unsecured debt issued		$ 572,000,000
Estimated weighted average life of student loans		5 years 21 days
Loans pledged as collateral					591,000,000
Principal amount of collateral					551,000,000
Capitalized interest					40,000,000
2023-A | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Basis spread on variable rate		1.53%
2023-C
Debt Instrument [Line Items]
Total Issued								$ 568,000,000
Private education loan term accounted for as a secured financing	$ 568,000,000
Loans sold to third parties	$ 568,000,000
Ownership interest percentage on asset-backed financing	100.00%
Unsecured debt issued	$ 568,000,000
Estimated weighted average life of student loans	4 years 11 months 4 days
Loans pledged as collateral					620,000,000
Principal amount of collateral					579,000,000
Capitalized interest					41,000,000
2023-C | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Basis spread on variable rate	1.69%
2022-C
Debt Instrument [Line Items]
Total Issued										$ 575,000,000
Private education loan term accounted for as a secured financing			$ 575,000,000
Loans sold to third parties			$ 575,000,000
Ownership interest percentage on asset-backed financing			100.00%
Unsecured debt issued			$ 575,000,000
Estimated weighted average life of student loans			4 years 8 months 8 days
Loans pledged as collateral						$ 543,000,000
Principal amount of collateral						513,000,000
Capitalized interest						$ 30,000,000
2022-C | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Basis spread on variable rate			1.76%
ABS Transactions
Debt Instrument [Line Items]
Private education loan term accounted for as a secured financing							$ 9,810,000,000
Private Education Loans
Debt Instrument [Line Items]
Private education loan term accounted for as a secured financing					4,020,000,000.00
Principal amount of collateral					3,900,000,000
Capitalized interest					$ 128,000,000