Securities - Additional Information (Detail) $ in Millions	6 Months Ended
Jun. 30, 2018 USD ($) loan position	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale [Line Items]
Loans pledged as collateral	$ 7,900
Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Number of fixed rate collateralized mortgage obligations \| loan	465
Weighted average maturity collateralized mortgage life	4 years 8 months 8 days
Residential Mortgage Backed Securities [Member] \| Agency residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Gross unrealized losses	$ 42	$ 20
Securities in unrealized loss positions, number of positions \| position	266
Weighted average maturity mortgage backed securities	3 years 11 months 23 days
Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Gross unrealized losses		$ 66
Commercial Mortgage Backed Securities [Member] \| Agency residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Gross unrealized losses	$ 108
Securities in unrealized loss positions, number of positions \| position	14
Weighted average maturity mortgage backed securities	4 years 21 days

Number of fixed-rate collateralized mortgage obligations.

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Weighted average maturity mortgage backed securities in years.

+ References

No definition available.

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- Definition

Weighted Average Maturity Mortgage Backed Securities

+ References

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- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

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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.

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