CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Financing Receivable, Troubled Debt Restructuring [Line Items]
Net charge-offs	$ 153	$ 74	$ 438	$ 182
Credit provision	172	123	516	342
Increase to ACL			78
Loans and leases	149,746		149,746		$ 156,662
Mortgage loans collateralized by OREO	321		321		250
Amortized cost basis	408		944
Charge-offs	191	116	551	308
TDR commitment to lend					81
Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring [Line Items]
Charge-offs				2
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Net charge-offs	70	15	198	36
Loans and leases	77,457		77,457		82,180
Amortized cost basis	365		836
Charge-offs	74	22	212	49
Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Net charge-offs	83	59	240	146
Loans and leases	72,289		72,289		74,482
Amortized cost basis	43		108
Charge-offs	117	$ 94	339	$ 259
Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases	46,753		46,753		51,836
Amortized cost basis	196		344
Charge-offs			97
Unfunded loan commitment
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis			146
Collateral Dependent | Home Equity Loan and Residential Mortgages | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases	542		542		561
Collateral Dependent | Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases	$ 293		$ 293		$ 21