Loans and Allowance for Credit Losses - Composition of Loan Portfolio (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 318,934	$ 312,028
Loans, percentage	100.00%	100.00%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 112,479	$ 106,912
Loans, percentage	35.30%	34.30%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 117,470	$ 112,023
Loans, percentage	36.90%	35.90%
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 39,191	$ 39,053
Loans, percentage	12.30%	12.50%
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 78,487	$ 76,493
Loans, percentage	24.60%	24.50%
Other Retail [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 61,623	$ 61,959
Loans, percentage	19.30%	19.90%
Lease Financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 4,991	$ 5,111
Loans, percentage	1.60%	1.60%
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 29,501	$ 28,757
Loans, percentage	9.30%	9.20%
Construction and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 9,690	$ 10,296
Loans, percentage	3.00%	3.30%
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 69,680	$ 67,546
Loans, percentage	21.80%	21.60%
Home Equity Loans, First Liens [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 8,807	$ 8,947
Loans, percentage	2.80%	2.90%
Credit Card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 22,163	$ 22,500
Loans, percentage	6.90%	7.20%
Retail Leasing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 6,941	$ 7,256
Loans, percentage	2.20%	2.30%
Home Equity and Second Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 10,457	$ 10,446
Loans, percentage	3.30%	3.40%
Revolving Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 2,652	$ 2,750
Loans, percentage	0.80%	0.90%
Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 16,732	$ 16,514
Loans, percentage	5.20%	5.30%
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 24,724	$ 24,866
Loans, percentage	7.80%	8.00%
Student [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 117	$ 127