Loans and Allowance for Credit Losses - Additional Information (Detail) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2022 USD ($) MortgageLoan	Sep. 30, 2022 USD ($) SecurityLoan MortgageLoan	Dec. 31, 2021 USD ($)
Loans and Allowance for Credit Losses [Line Items]
Loans pledged at the Federal Reserve Bank	$ 84,000	$ 84,000	$ 76,900
Unearned interest and deferred fees and costs on originated loans	331	331	475
Foreclosed residential real estate property included in other real estate owned	24	24	22
Foreclosed residential real estate related to mortgage loans whose payments are insured by the Federal Housing Administration or guaranteed by the United States Department of Veterans Affairs	46	46	22
Residential mortgage loans secured by residential real estate in process of foreclosure	$ 1,100	$ 1,100	696
Number of residential mortgage loans, home equity and second mortgage loans, and GNMA loans where trial period was unsuccessful and no longer eligible for a permanent modification \| MortgageLoan	17	45
Outstanding balance of residential mortgage loans, home equity and second mortgage loans, and GNMA loans where trial period was unsuccessful and no longer eligible for a permanent modification	$ 3	$ 7
Commitments to lend additional funds	40	40
Allowance For Individually Evaluated Loans		5
Federal Home Loan Bank Advances [Member]
Loans and Allowance for Credit Losses [Line Items]
Loans pledged at the Federal Home Loan Bank	98,200	98,200	92,100
Government National Mortgage Association [Member]
Loans and Allowance for Credit Losses [Line Items]
Residential mortgage loans secured by residential real estate in process of foreclosure	$ 841	$ 841	$ 555
Home Equity and Second Mortgages [Member]
Loans and Allowance for Credit Losses [Line Items]
Number of loans in trial period \| SecurityLoan		7
Outstanding balance of loans in trial period		$ 1
Estimated post-modification balance of loans in trial period		$ 1
Residential Mortgages [Member]
Loans and Allowance for Credit Losses [Line Items]
Number of loans in trial period \| SecurityLoan		9
Outstanding balance of loans in trial period		$ 1
Estimated post-modification balance of loans in trial period		$ 1
Government National Mortgage Association [Member]
Loans and Allowance for Credit Losses [Line Items]
Number of loans in trial period \| SecurityLoan		64
Outstanding balance of loans in trial period		$ 8
Estimated post-modification balance of loans in trial period		$ 8

Amount of financing receivable modified on trial basis.

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