Fair Value Measurements - Additional Information (Detail)	9 Months Ended
Sep. 30, 2017 USD ($) security	Dec. 31, 2016 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale adjusted to fair value	$ 0	$ 0
Fair value of OREO property re-evaluated period	90 days
Third party broker price opinion periodic review period	180 days
Loans, net of allowance	$ 85,612,000,000	85,180,000,000
Loans at fair value	2,000,000
Discontinued Operations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans at fair value	2,000,000	3,000,000
Discontinued Operations [Member] \| Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	1,400,000,000	1,600,000,000
Loans at fair value	2,000,000	3,000,000
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities measured at fair value on non recurring basis	0	0
Loans held for sale adjusted to fair value	1,341,000,000	1,104,000,000
Loans at fair value	84,211,000,000	83,285,000,000
Fair Value [Member] \| Discontinued Operations [Member] \| Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	1,200,000,000	1,300,000,000
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	85,612,000,000	85,180,000,000
Carrying Amount [Member] \| Discontinued Operations [Member] \| Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans, net of allowance	$ 1,400,000,000	1,500,000,000
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Number of convertible preferred securities \| security	2
Level 3 [Member] \| Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale adjusted to fair value	$ 1,283,000,000	1,042,000,000
Loans at fair value	84,211,000,000	83,285,000,000
Consumer Portfolio Segment [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Real estate — residential mortgage	$ 5,476,000,000	$ 5,547,000,000

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Number of Convertible Preferred Securities

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Period for evaluation of fair value of property.

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

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Amount before allowance of consumer mortgage. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes subordinated loans such as home equity lines of credit and 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 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&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(a)(3),(b))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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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=82891408&loc=d3e4428-111522

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
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-Paragraph 1
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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

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