Securities - Additional Information (Detail)	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($) security	Jun. 30, 2017 USD ($) security	Jun. 30, 2018 USD ($) security	Jun. 30, 2017 USD ($) security	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale [Line Items]
Increase in credit losses for which an other-than-temporary impairment was previously recognized	$ 0	$ 0	$ 0	$ 0
Securities with changes to other than temporary impairment estimates related to credit component \| security	0	0	0	0
Other assets [Member]
Debt Securities, Available-for-sale [Line Items]
Equity securities carried at fair value	$ 283,000,000		$ 283,000,000
Equity securities without readily determinable fair values	5,000,000		5,000,000
Federal Home Loan Bank Stock	201,000,000		201,000,000		$ 201,000,000
Federal Reserve Bank Stock	$ 631,000,000		$ 631,000,000		$ 631,000,000

Asset Backed Securities With Changes to Other Than Temporary Impairment Estimates Related to Credit Component

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- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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- Definition

Amount of investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117539-209714

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- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 325
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75031641&loc=d3e63345-112809

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- Definition

Federal Reserve Bank stock represents an equity interest in the Federal Reserve Bank. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

+ Details

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- Definition

This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which a previous OTTI was recognized and the investor does not intend to sell the debt security and it is not more likely than not that the investor will be required to sell the debt security before recovery of its amortized cost basis.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

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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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