Borrowings - Unconsolidated VIEs Narrative (Details) - USD ($) $ in Millions					12 Months Ended
	May 24, 2023	Oct. 19, 2022	May 27, 2022	Mar. 16, 2022	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Vertical risk retention interest					5.00%	5.00%
2023-B
Debt Instrument [Line Items]
Vertical risk retention interest					5.00%
2023-B | Student Loan
Debt Instrument [Line Items]
Private education loans sold	$ 2,000
Additional net proceeds from sales of loans held for investment, capitalized interest	105
Gain on sale	5
2023-D
Debt Instrument [Line Items]
Vertical risk retention interest					5.00%
2023-D | Student Loan
Debt Instrument [Line Items]
Private education loans sold	1,000
Additional net proceeds from sales of loans held for investment, capitalized interest	53
Gain on sale	$ 1
2022-A
Debt Instrument [Line Items]
Vertical risk retention interest				5.00%
2022-A | Student Loan
Debt Instrument [Line Items]
Private education loans sold				$ 973
Additional net proceeds from sales of loans held for investment, capitalized interest				95
Gain on sale				$ 10
2022-B
Debt Instrument [Line Items]
Vertical risk retention interest			5.00%
2022-B | Student Loan
Debt Instrument [Line Items]
Private education loans sold			$ 2,000
Additional net proceeds from sales of loans held for investment, capitalized interest			107
Gain on sale			$ 11
2022-D
Debt Instrument [Line Items]
Vertical risk retention interest			5.00%
2022-D | Student Loan
Debt Instrument [Line Items]
Private education loans sold		$ 1,000
Additional net proceeds from sales of loans held for investment, capitalized interest		54
Gain on sale		$ 3