Education Loans - Education Loan Portfolio by Program (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Accounts Notes And Loans Receivable [Line Items]
Loans, net	$ 105,122	$ 111,070
Percentage to total education loans	100.00%	100.00%
Average Balance education loans	$ 108,751	$ 117,858
Average Effective Interest Rate of education loans	3.98%	3.49%
FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, net	$ 81,703	$ 87,730
Stafford And Other Education Loans [Member] \| FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, net	$ 28,409	$ 32,319
Percentage to total education loans	27.00%	29.00%
Average Balance education loans	$ 30,462	$ 34,710
Average Effective Interest Rate of education loans	2.94%	2.31%
Consolidation Loans Member \| FFELP Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, net	$ 53,294	$ 55,411
Percentage to total education loans	51.00%	50.00%
Average Balance education loans	$ 54,527	$ 57,787
Average Effective Interest Rate of education loans	3.30%	2.98%
Private Education Loans [Member]
Accounts Notes And Loans Receivable [Line Items]
Loans, net	$ 23,419	$ 23,340
Percentage to total education loans	22.00%	21.00%
Average Balance education loans	$ 23,762	$ 25,361
Average Effective Interest Rate of education loans	6.88%	6.26%

Represents the average balance of outstanding student loans during the period presented.

No definition available.

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- Definition

Percentage to total student loans.

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes loans held for sale. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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- Definition

Yield on the receivable, on which interest has been imputed, as calculated from its issuance value or purchase price. The calculated effective interest rate considers factors such as the issued face value or price paid for the receivable, the time period between payments, and the time until maturity [full receipt] of the receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

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- Details

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- Details

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