Loans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Accrued interest receivable	$ 1,300	$ 1,300
TDRs	2,100	2,100	$ 1,700
Commitments to lend on loans modified in TDRs	168	168	178
Federal Home Loan banks
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans Pledged as Collateral	15,000	15,000	14,600
Line of Credit Facility, Remaining Borrowing Capacity	16,200	16,200	18,700
Federal Reserve Discount Window
Financing Receivable, Allowance for Credit Loss [Line Items]
Loans Pledged as Collateral	26,600	26,600	6,700
Line of Credit Facility, Remaining Borrowing Capacity	21,000	21,000	5,300
Credit Card and Consumer Banking \| Performing
Financing Receivable, Allowance for Credit Loss [Line Items]
TDRs	1,200	1,200	1,100
Commercial Banking \| Performing
Financing Receivable, Allowance for Credit Loss [Line Items]
TDRs	438	438	$ 224
Domestic credit card: \| Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Revolving loans converted to term during period	$ 250	$ 499

Amount, before allowance for credit loss, of accrued interest on financing receivable.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Section 50
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Amount of financing receivable modified as troubled debt restructuring.

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Amount of increase in term loan from conversion of revolving financing receivable.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Amount of unfunded portion of contractual agreement to lend funds to borrower for financing receivable modified as troubled debt restructuring.

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