Borrowings - Pre-2019 Transactions (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2018
ABS Transactions
Debt Instrument [Line Items]
Private education loan term accounted for as a secured financing		$ 5,800
Private Education Loans
Debt Instrument [Line Items]
Private education loan term accounted for as a secured financing	$ 3,700
Principal amount of collateral	3,500
Capitalized interest	$ 159

This is the principal amount outstanding for loans which are in the process of being securitized as of the date of the statement of financial position (across all types of loans).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

Name:	us-gaap_PrincipalAmountOutstandingOnLoansHeldForSaleOrSecuritization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant