Loans and Allowance for Credit Losses - Composition of Loan Portfolio (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 332,369	$ 312,028
Loans, percentage	100.00%	100.00%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 121,130	$ 106,912
Loans, percentage	36.40%	34.30%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 125,983	$ 112,023
Loans, percentage	37.90%	35.90%
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 39,753	$ 39,053
Loans, percentage	12.00%	12.50%
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 82,114	$ 76,493
Loans, percentage	24.70%	24.50%
Other Retail [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 60,822	$ 61,959
Loans, percentage	18.30%	19.90%
Lease Financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 4,853	$ 5,111
Loans, percentage	1.50%	1.60%
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 29,864	$ 28,757
Loans, percentage	9.00%	9.20%
Construction and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 9,889	$ 10,296
Loans, percentage	3.00%	3.30%
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 73,522	$ 67,546
Loans, percentage	22.10%	21.60%
Home Equity Loans, First Liens [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 8,592	$ 8,947
Loans, percentage	2.60%	2.90%
Credit Card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 23,697	$ 22,500
Loans, percentage	7.10%	7.20%
Retail Leasing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,490	$ 7,256
Loans, percentage	2.00%	2.30%
Home Equity and Second Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 10,973	$ 10,446
Loans, percentage	3.30%	3.40%
Revolving Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 2,764	$ 2,750
Loans, percentage	0.80%	0.90%
Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 16,656	$ 16,514
Loans, percentage	5.00%	5.30%
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 23,830	$ 24,866
Loans, percentage	7.20%	8.00%
Student [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 109	$ 127