CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Troubled Debt Restructurings, Modified Default (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	$ 128	$ 57	$ 224	$ 86
Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	3	1	6	1
Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	89	48	166	77
Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	21	1	34	1
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	2	7
Term Extension and Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	15		16
Commercial
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	115	41	181	70
Commercial | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1	0	1	0
Commercial | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	78	41	144	70
Commercial | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	21	0	21	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	0
Commercial | Term Extension and Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	15		15
Commercial | Commercial and industrial
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	19	0	19	3
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	1	0	1	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	3	0	3	3
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	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	0
Commercial | Commercial and industrial | Term Extension and Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	15		15
Commercial | Commercial real estate
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	96	41	162	67
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	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	75	41	141	67
Commercial | Commercial real estate | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	21	0	21	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	0
Commercial | Commercial real estate | Term Extension and Payment Delay
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	13	16	43	16
Retail | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	2	1	5	1
Retail | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	11	7	22	7
Retail | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	1	13	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	2	7
Retail | Term Extension and Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0		1
Retail | Residential mortgages
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	11	12	25	12
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	1	0	1
Retail | Residential mortgages | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	11	6	22	6
Retail | Residential mortgages | Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	0	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		5	1	5
Retail | Residential mortgages | Term Extension and Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0		1
Retail | Home equity
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	3	1	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	0	0	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	1	0	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	0	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		2	1	2
Retail | Home equity | Term Extension and Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0		0
Retail | Automobile
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	0	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	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	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	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	0
Retail | Automobile | Term Extension and Payment Delay
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	1	1	16	1
Retail | Education | Interest Rate Reduction
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1	0	4	0
Retail | Education | Term Extension
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	0	0	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	1	12	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	0	0
Retail | Education | Term Extension and 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
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	1	0	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	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	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	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	$ 0
Retail | Other retail | Term Extension and Payment Delay
Financing Receivable, Modified, Subsequent Default [Line Items]
Amortized cost basis of modified loans that are in subsequent default	$ 0		$ 0