Allowance for Credit Losses - Narrative (Details)	6 Months Ended
	Jun. 30, 2022 USD ($) payment termChange	Jul. 01, 2006
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable allowance period increase	$ 285,000,000
Partially offset by negative provisions	$ 2,240,000,000
Interest rate offered to borrowers facing financial difficulty, period	2 years
Number of term changes | termChange	2
Criteria for loans to be considered as nonperforming (greater than)	90 days
Tier 1 of government guarantee (at least)	97.00%	97.00%
Maximum amount of forbearance granted	12 months
Number of monthly payments required by a borrower between successive grants of forbearance | payment	12
Threshold period for payment default	60 days
Percentage of FFELP loans insured and guaranteed (at least)	97.00%
Period of loans past due that have accrued interest (greater than)	90 days
Monthly payment that is smaller than the interest accrued on the loan in that month	$ 25
Private Education Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period when delinquent loans are written off	120 days
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate offered to borrowers facing financial difficulty	4.00%
Increments in which forbearance is granted	2 months
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Increments in which forbearance is granted	1 month