Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Securities held to maturity, mortgaged related securities, pledged	$ 704,000,000	$ 898,000,000
Securities available for sale, other securities, pledged	464,000,000	380,000,000
Loans pledged to FHLB, collateral for wholesale borrowings	33,900,000,000	33,500,000,000
Commitments	3,112,000,000
Commitments to purchase securities	0
Total loan commitments
Loss Contingencies [Line Items]
Commitments	2,821,000,000	2,500,000,000
Commercial, performance stand-by, and financial stand-by letters of credit
Loss Contingencies [Line Items]
Commitments	$ 291,000,000	$ 376,000,000

Fair value portion of arrangements with third parties, including, but not limited to, operating lease arrangement and arrangement in which the entity has agreed to expend funds to procure goods or services, or has agreed to commit resources to supply goods or services.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(25))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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- Definition

The minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

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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

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- Definition

The carrying amount as of the date of the latest financial statement presented of mortgage-related securities classified as held to maturity which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729

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- Definition

The carrying amount as of the date of the latest financial statement presented of other securities classified as available for sale or held for investment which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

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- Definition

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for FHLB debt obligations, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

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