Loans and Allowance for Credit Losses - Summary of Loans Modified as TDRs in the Past Twelve Months that have Subsequently Defaulted (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	2,163	2,383	4,180	4,764
Amount Defaulted | $	$ 38	$ 30	$ 63	$ 71
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	175	327	389	612
Amount Defaulted | $	$ 3	$ 8	$ 6	$ 24
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2	5	5	12
Amount Defaulted | $	$ 1	$ 1	$ 2	$ 6
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	79	12	113	27
Amount Defaulted | $	$ 7	$ 1	$ 10	$ 3
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	60	191	143	471
Amount Defaulted | $	$ 1	$ 3	$ 2	$ 8
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,727	1,805	3,361	3,569
Amount Defaulted | $	$ 9	$ 11	$ 18	$ 20
Total Loans, Excluding Loans Purchased from GNMA Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,043	2,340	4,011	4,691
Amount Defaulted | $	$ 21	$ 24	$ 38	$ 61
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	120	43	169	73
Amount Defaulted | $	$ 17	$ 6	$ 25	$ 10