Loans and Allowance for Credit Losses - Composition of Loan Portfolio (Detail) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 375,234	$ 388,213
Loans, percentage		100.00%	100.00%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 129,040	$ 131,128
Loans, percentage		34.40%	33.80%
Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 133,319	$ 135,690
Loans, percentage		35.50%	35.00%
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 54,131	$ 55,487
Loans, percentage		14.40%	14.30%
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[1],[2]	$ 115,055	$ 115,845
Loans, percentage		30.70%	29.80%
Other Retail [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 45,649	$ 54,896
Loans, percentage		12.20%	14.10%
Lease Financing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 4,279	$ 4,562
Loans, percentage		1.10%	1.20%
Commercial Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 42,473	$ 43,765
Loans, percentage		11.30%	11.30%
Construction and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 11,658	$ 11,722
Loans, percentage		3.10%	3.00%
Residential Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 107,875	$ 107,858
Loans, percentage		28.80%	27.80%
Home Equity Loans, First Liens [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 7,180	$ 7,987
Loans, percentage		1.90%	2.00%
Credit Card [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	[3]	$ 27,080	$ 26,295
Loans, percentage		7.20%	6.80%
Retail Leasing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 4,271	$ 5,519
Loans, percentage		1.20%	1.40%
Home Equity and Second Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 12,879	$ 12,863
Loans, percentage		3.40%	3.30%
Revolving Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 3,766	$ 3,983
Loans, percentage		1.00%	1.00%
Installment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 14,145	$ 14,592
Loans, percentage		3.80%	3.80%
Automobile [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans		$ 10,588	$ 17,939
Loans, percentage		2.80%	4.60%

[1] At September 30, 2023, $2.0 billion of GNMA loans 90 days or more past due and $963 million of modified GNMA loans whose repayments are insured by the Federal Housing Administration or guaranteed by the United States Department of Veterans Affairs were classified with a pass rating, compared with $2.2 billion and $1.0 billion at December 31, 2022, respectively.

[2] At September 30, 2023, $558 million of loans 30–89 days past due and $2.0 billion of loans 90 days or more past due purchased and that could be purchased from Government National Mortgage Association (“GNMA”) mortgage pools under delinquent loan repurchase options whose repayments are insured by the Federal Housing Administration or guaranteed by the United States Department of Veterans Affairs, were classified as current, compared with $647 million and $2.2 billion at December 31, 2022, respectively.

[3] Predominately all credit card loans are considered revolving loans. Includes an immaterial amount of revolving converted to term loans.