CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Narrative (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Financing Receivable, Troubled Debt Restructuring [Line Items]
Net charge-offs		$ 152	$ 49	$ 285	$ 108
Credit provision		176	216	344	219
Increase to ACL				59
Loans and leases	[1]	151,320		151,320		$ 156,662
Mortgage loans collateralized by OREO		307		307		250
Amortized cost basis		461		617
Charge-offs		189	91	360	192
TDR commitment to lend						81
Troubled Debt Restructuring
Financing Receivable, Troubled Debt Restructuring [Line Items]
Charge-offs			1		2
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Net charge-offs		76	10	128	21
Loans and leases		78,279		78,279		82,180
Amortized cost basis		424		550
Charge-offs		79	13	138	27
Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Net charge-offs		76	39	157	87
Loans and leases		73,041		73,041		74,482
Amortized cost basis		37		67
Charge-offs		110	$ 78	222	$ 165
Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases		48,038		48,038		51,836
Amortized cost basis		125		214
Charge-offs				72
Unfunded loan commitment
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis				76
Collateral Dependent | Home Equity Loan and Residential Mortgages | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases		547		547		561
Collateral Dependent | Commercial and industrial | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Loans and leases		$ 288		$ 288		$ 21

[1] Includes amounts in consolidated VIEs. See Note 6 for additional information.