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Allowance for Loan Losses - Loan Type (Detail) - FFELP Loans [Member] - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable Recorded Investment Past Due [Line Items]
Total loans, gross	$ 55,827	$ 61,223
Change	(5,396)
Stafford Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total loans, gross	16,996	18,364
Change	(1,368)
Consolidation Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total loans, gross	34,011	37,829
Change	(3,818)
Rehab Loans [Member]
Financing Receivable Recorded Investment Past Due [Line Items]
Total loans, gross	4,820	$ 5,030
Change	$ (210)

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- Definition

Financing receivable before allowance for credit loss and fee change amount

+ References

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- Definition

Amount, before allowance for credit loss, of financing receivable.

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