CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Troubled Debt Restructurings, Modified Default (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	$ 82	$ 80
Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	2	2
Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	76	78
Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1	0
Interest Rate Reduction and Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	3	0
Commercial
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	71	72
Commercial | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	0
Commercial | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	71	72
Commercial | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	0
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	0
Commercial | Commercial and industrial
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	34
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	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	34
Commercial | Commercial and industrial | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	0
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	0
Commercial | Commercial real estate
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	71	38
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	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	71	38
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	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	0
Retail
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	11	8
Retail | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	2	2
Retail | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	5	6
Retail | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1	0
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	3	0
Retail | Residential mortgages
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	8	6
Retail | Residential mortgages | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	0
Retail | Residential mortgages | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	5	6
Retail | Residential mortgages | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1	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	2	0
Retail | Home equity
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	2	0
Retail | Home equity | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1	0
Retail | Home equity | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	0
Retail | Home equity | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	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	1	0
Retail | Automobile
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	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	0
Retail | Automobile | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	0
Retail | Automobile | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	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	0
Retail | Education
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	2
Retail | Education | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	2
Retail | Education | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	0
Retail | Education | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	0
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	0
Retail | Other retail
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1	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	1	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	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	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	$ 0