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
	Mar. 31, 2022 USD ($) SecurityLoan	Mar. 31, 2021 USD ($) SecurityLoan
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	2,017	2,381
Amount Defaulted | $	$ 25	$ 41
Commercial [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	214	285
Amount Defaulted | $	$ 3	$ 16
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	3	7
Amount Defaulted | $	$ 1	$ 5
Residential Mortgages [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	34	15
Amount Defaulted | $	$ 3	$ 2
Other Retail [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	83	280
Amount Defaulted | $	$ 1	$ 5
Credit Card [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,634	1,764
Amount Defaulted | $	$ 9	$ 9
Total Loans, Excluding Loans Purchased from GNMA Mortgage Pools [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	1,968	2,351
Amount Defaulted | $	$ 17	$ 37
Government National Mortgage Association [Member]
Financing Receivable, Modifications [Line Items]
Number of Loans | SecurityLoan	49	30
Amount Defaulted | $	$ 8	$ 4