Loans and Allowance for Credit Losses - Composition of Loan Portfolio (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 342,708	$ 312,028
Loans, percentage	100.00%	100.00%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 126,930	$ 106,912
Loans, percentage	37.00%	34.30%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 131,687	$ 112,023
Loans, percentage	38.40%	35.90%
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 40,329	$ 39,053
Loans, percentage	11.70%	12.50%
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 86,274	$ 76,493
Loans, percentage	25.20%	24.50%
Other Retail [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 59,880	$ 61,959
Loans, percentage	17.50%	19.90%
Lease Financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 4,757	$ 5,111
Loans, percentage	1.40%	1.60%
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 30,223	$ 28,757
Loans, percentage	8.80%	9.20%
Construction and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 10,106	$ 10,296
Loans, percentage	2.90%	3.30%
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 78,006	$ 67,546
Loans, percentage	22.80%	21.60%
Home Equity Loans, First Liens [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 8,268	$ 8,947
Loans, percentage	2.40%	2.90%
Credit Card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 24,538	$ 22,500
Loans, percentage	7.20%	7.20%
Retail Leasing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,037	$ 7,256
Loans, percentage	1.80%	2.30%
Home Equity and Second Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 11,367	$ 10,446
Loans, percentage	3.30%	3.40%
Revolving Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 2,721	$ 2,750
Loans, percentage	0.80%	0.90%
Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 16,417	$ 16,514
Loans, percentage	4.80%	5.30%
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 23,236	$ 24,866
Loans, percentage	6.80%	8.00%
Student [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 102	$ 127