CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Troubled Debt Restructurings, Modified Default (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	$ 164	$ 242
Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1
Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	112
Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	44
Interest Rate Reduction and Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	7
Commercial
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	145
Commercial | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Commercial | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	102
Commercial | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	43
Commercial | Interest Rate Reduction and Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Commercial | Commercial and industrial
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	43	0
Commercial | Commercial and industrial | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Commercial | Commercial and industrial | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Commercial | Commercial and industrial | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	43
Commercial | Commercial and industrial | Interest Rate Reduction and Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Commercial | Commercial real estate
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	102
Commercial | Commercial real estate | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Commercial | Commercial real estate | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	102
Commercial | Commercial real estate | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Commercial | Commercial real estate | Interest Rate Reduction and Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	19
Retail | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1
Retail | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	10
Retail | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1
Retail | Interest Rate Reduction and Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	7
Retail | Residential mortgages
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	15	$ 242
Retail | Residential mortgages | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1
Retail | Residential mortgages | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	9
Retail | Residential mortgages | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Residential mortgages | Interest Rate Reduction and Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	5
Retail | Home equity
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	3
Retail | Home equity | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Home equity | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1
Retail | Home equity | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Home equity | Interest Rate Reduction and Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	2
Retail | Automobile
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Automobile | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Automobile | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Automobile | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Automobile | Interest Rate Reduction and Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Education
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1
Retail | Education | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Education | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Education | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1
Retail | Education | Interest Rate Reduction and Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Other retail
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Other retail | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Other retail | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Other retail | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0
Retail | Other retail | Interest Rate Reduction and Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	$ 0