Business Combinations, Goodwill and Acquired Intangible - Summary of Goodwill for Each Reporting Units and Reportable Segments (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Goodwill [Line Items]
Goodwill	$ 670	$ 670
Federal Education Loans [Member]
Goodwill [Line Items]
Goodwill	232	232
Federal Education Loans [Member] | FFELP Loans [Member]
Goodwill [Line Items]
Goodwill	227	227
Federal Education Loans [Member] | Federal Education Loan Servicing [Member]
Goodwill [Line Items]
Goodwill	5	5
Consumer Lending Segment [Member]
Goodwill [Line Items]
Goodwill	196	196
Consumer Lending Segment [Member] | Private Education Legacy In-School Loans [Member]
Goodwill [Line Items]
Goodwill	106	106
Consumer Lending Segment [Member] | Private Education Refinance Loans [Member]
Goodwill [Line Items]
Goodwill	77	77
Consumer Lending Segment [Member] | Private Education Recent In-School Loans [Member]
Goodwill [Line Items]
Goodwill	13	13
Business Processing [Member]
Goodwill [Line Items]
Goodwill	242	242
Business Processing [Member] | Government Services [Member]
Goodwill [Line Items]
Goodwill	136	136
Business Processing [Member] | Healthcare Services [Member]
Goodwill [Line Items]
Goodwill	$ 106	$ 106