Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs (Detail) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2022 USD ($) SecurityLoan	Jun. 30, 2021 USD ($) SecurityLoan	Jun. 30, 2022 USD ($) SecurityLoan	Jun. 30, 2021 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	10,705	6,912	22,520	15,678
Pre-Modification Outstanding Loan Balance	$ 286	$ 307	$ 705	$ 729
Post-Modification Outstanding Loan Balance	$ 275	$ 311	$ 685	$ 701
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	506	526	1,015	1,230
Pre-Modification Outstanding Loan Balance	$ 50	$ 12	$ 88	$ 87
Post-Modification Outstanding Loan Balance	$ 41	$ 13	$ 73	$ 73
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	28	30	37	86
Pre-Modification Outstanding Loan Balance	$ 11	$ 38	$ 22	$ 124
Post-Modification Outstanding Loan Balance	$ 9	$ 41	$ 19	$ 112
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	366	360	1,206	696
Pre-Modification Outstanding Loan Balance	$ 106	$ 141	$ 334	$ 245
Post-Modification Outstanding Loan Balance	$ 106	$ 140	$ 332	$ 244
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	756	468	1,484	1,793
Pre-Modification Outstanding Loan Balance	$ 24	$ 18	$ 61	$ 55
Post-Modification Outstanding Loan Balance	$ 20	$ 17	$ 57	$ 49
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	8,696	5,050	18,035	10,836
Pre-Modification Outstanding Loan Balance	$ 48	$ 31	$ 98	$ 64
Post-Modification Outstanding Loan Balance	$ 49	$ 31	$ 99	$ 65
Total Loans, Excluding Loans Purchased from GNMA Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	10,352	6,434	21,777	14,641
Pre-Modification Outstanding Loan Balance	$ 239	$ 240	$ 603	$ 575
Post-Modification Outstanding Loan Balance	$ 225	$ 242	$ 580	$ 543
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans \| SecurityLoan	353	478	743	1,037
Pre-Modification Outstanding Loan Balance	$ 47	$ 67	$ 102	$ 154
Post-Modification Outstanding Loan Balance	$ 50	$ 69	$ 105	$ 158

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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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