CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases	$ 145,959	$ 156,662
Mortgage loans collateralized by residential real estate property	336	250
Net charge-offs	609	270	$ 325
Provision (benefit) for credit losses	687	474	(411)
Allowance for credit losses	78
Modified TDRs charge-offs	757	434	539
Unfunded commitments related to TDRs	221	81
Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring [Line Items]
Modified TDRs charge-offs		3
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Allowance for credit losses, individually evaluated for impairment	5
Loans and leases	74,445	82,180
Net charge-offs	267	52	164
Modified TDRs charge-offs	285	70	218
Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases	71,514	74,482
Net charge-offs	342	218	161
Modified TDRs charge-offs	472	364	$ 321
Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases	43,826	51,836
Modified TDRs charge-offs	121
Collateral Dependent | Home Equity Loan And Residential Mortgages | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases	556	561
Collateral Dependent | Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases	$ 233	$ 21