Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs (Detail) $ in Millions	3 Months Ended
Mar. 31, 2022 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	11,815
Pre-Modification Outstanding Loan Balance	$ 419
Post-Modification Outstanding Loan Balance	$ 410
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	509
Pre-Modification Outstanding Loan Balance	$ 38
Post-Modification Outstanding Loan Balance	$ 32
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	9
Pre-Modification Outstanding Loan Balance	$ 11
Post-Modification Outstanding Loan Balance	$ 10
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	840
Pre-Modification Outstanding Loan Balance	$ 228
Post-Modification Outstanding Loan Balance	$ 226
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	728
Pre-Modification Outstanding Loan Balance	$ 37
Post-Modification Outstanding Loan Balance	$ 37
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	9,339
Pre-Modification Outstanding Loan Balance	$ 50
Post-Modification Outstanding Loan Balance	$ 50
Total Loans, Excluding Loans Purchased from GNMA Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	11,425
Pre-Modification Outstanding Loan Balance	$ 364
Post-Modification Outstanding Loan Balance	$ 355
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	390
Pre-Modification Outstanding Loan Balance	$ 55
Post-Modification Outstanding Loan Balance	$ 55

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

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Amount, after troubled debt restructuring, of modified financing receivable.

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