Securities - Additional Information (Detail)	3 Months Ended	6 Months Ended
Jun. 30, 2017 USD ($) security	Jun. 30, 2016 USD ($) security	Jun. 30, 2017 USD ($) security	Jun. 30, 2016 USD ($) security	Dec. 31, 2016 USD ($)
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Securities with changes to other than temporary impairment estimates related to credit component \| security	0	0	0	0
Increase in credit losses for which an other-than-temporary impairment was previously recognized	$ 0	$ 0	$ 0	$ 0
Other assets [Member]
Schedule of Available-for-sale and Held-to-Maturity Securities [Line Items]
Federal Home Loan Bank Stock	295,000,000		295,000,000		$ 338,000,000
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

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://www.xbrl.org/2003/role/presentationRef
-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

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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://www.xbrl.org/2003/role/presentationRef
-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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