Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs (Detail) $ in Millions	3 Months Ended
Mar. 31, 2022 USD ($) SecurityLoan	Mar. 31, 2021 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	11,815	8,766
Pre-Modification Outstanding Loan Balance	$ 419	$ 422
Post-Modification Outstanding Loan Balance	$ 410	$ 390
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	509	704
Pre-Modification Outstanding Loan Balance	$ 38	$ 75
Post-Modification Outstanding Loan Balance	$ 32	$ 60
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	9	56
Pre-Modification Outstanding Loan Balance	$ 11	$ 86
Post-Modification Outstanding Loan Balance	$ 10	$ 71
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	840	336
Pre-Modification Outstanding Loan Balance	$ 228	$ 104
Post-Modification Outstanding Loan Balance	$ 226	$ 104
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	728	1,325
Pre-Modification Outstanding Loan Balance	$ 37	$ 37
Post-Modification Outstanding Loan Balance	$ 37	$ 32
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	9,339	5,786
Pre-Modification Outstanding Loan Balance	$ 50	$ 33
Post-Modification Outstanding Loan Balance	$ 50	$ 34
Total Loans, Excluding Loans Purchased from GNMA Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	11,425	8,207
Pre-Modification Outstanding Loan Balance	$ 364	$ 335
Post-Modification Outstanding Loan Balance	$ 355	$ 301
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	390	559
Pre-Modification Outstanding Loan Balance	$ 55	$ 87
Post-Modification Outstanding Loan Balance	$ 55	$ 89

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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 http://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

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