Fair Value Measurements - Additional Information (Detail) - USD ($)	9 Months Ended
Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities measured at fair value on non recurring basis	$ 0	$ 0	$ 0
Loans held for sale adjusted to fair value	$ 0	0	0
Fair value of OREO property re-evaluated period	90 days
Loans, net of allowance	$ 59,295,000,000	56,587,000,000	55,351,000,000
Loan securitization trust VIEs, fair value	$ 169,000,000
Loans in portfolio		191,000,000	201,000,000
Average maturity of short-term financial instruments	Less than six months
Residential Real Estate Mortgage Loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	$ 2,300,000,000	2,200,000,000	2,200,000,000
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale adjusted to fair value	916,000,000	734,000,000	784,000,000
Fair Value [Member] \| Discontinued Operations [Member] \| Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	1,500,000,000	1,800,000,000	1,900,000,000
Loans in portfolio		191,000,000	201,000,000
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	59,295,000,000	56,587,000,000	55,351,000,000
Carrying Amount [Member] \| Discontinued Operations [Member] \| Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	$ 1,900,000,000	$ 2,100,000,000	$ 2,100,000,000

Average maturity of short term financial instrument.

No definition available.

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- Definition

Loans in portfolio.

+ References

No definition available.

+ Details

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- Definition

Loan securitization trust vies held for sale fair value.

+ References

No definition available.

+ Details

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- Definition

Period for evaluation of fair value of property.

+ References

No definition available.

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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.

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- Definition

Aggregation of the liabilities reported on the balance sheet measured at fair value on a nonrecurring basis by the entity.

+ References

No definition available.

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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. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

Reference 2: 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)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

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