Borrowings - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Contractual interest rates of long-term agreements to repurchase securities		4.29%
Collateral posted		$ 108,000,000
Debt Maturity, Start Year	Jan. 01, 2027
Debt Maturity, End Year	Dec. 31, 2033
Minimum [Member]
Debt Instrument [Line Items]
Variable interest rate of Senior Notes /Junior Subordinated Debentures	1.06%	2.76%
Maximum [Member]
Debt Instrument [Line Items]
Variable interest rate of Senior Notes /Junior Subordinated Debentures	3.59%	5.34%
FHLBs Facility [Member]
Debt Instrument [Line Items]
Borrowing facilities available with FHLB's amount	$ 19,000,000,000.0
Federal Reserve Bank of New York [Member]
Debt Instrument [Line Items]
Line of credit facility	$ 13,000,000,000.0
Senior Notes Issued in July 2018 [Member]
Debt Instrument [Line Items]
Variable interest rate of Senior Notes /Junior Subordinated Debentures	0.90%	2.62%
Variable Rate Senior Notes [Member]
Debt Instrument [Line Items]
Weighted-average variable rates payable	0.63%	2.34%
Variable Rate Senior Notes [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Variable interest rate of Senior Notes /Junior Subordinated Debentures	0.49%	2.21%
Variable Rate Senior Notes [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Variable interest rate of Senior Notes /Junior Subordinated Debentures	0.83%	2.54%
Long Term Fixed Rate Advances From Fhlb
Debt Instrument [Line Items]
Advances from the FHLB earliest maturity date	2029
Advances from the FHLB latest maturity date,	2035
Long Term Fixed Rate Advances From Fhlb \| Weighted Average [Member]
Debt Instrument [Line Items]
Variable contractual interest rate of long-term debt	5.82%	5.82%
Subordinated Capital Notes [Member]
Debt Instrument [Line Items]
Interest rate of debt instrument		3.02%
Subordinated Variable Rate Notes Due 2021 [Member]
Debt Instrument [Line Items]
Interest rate of debt instrument	0.87%	2.55%
Junior Subordinated Debt [Member]
Debt Instrument [Line Items]
Weighted-average variable rates payable	1.65%	3.37%
Short-term Borrowings [Member]
Debt Instrument [Line Items]
Stated maturity	1 year

Contractual interest rates of long-term agreements to repurchase securities.

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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Contractual interest rate for funds borrowed, under the debt agreement.

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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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Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

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Earliest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average interest rate of debt outstanding.

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- Definition

The earliest year of maturity for the advances from the Federal Home Loan Bank as of the Balance Sheet date.

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The last year of maturity for the advances from the Federal Home Loan Bank as of the Balance Sheet date.

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States the interest rate applicable to Federal Home Loan Bank advances outstanding as of the Balance Sheet date.

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Fair value of securities pledged as collateral against securities sold under agreement to repurchase.

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