CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Modified (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2023
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 461,000,000	$ 617,000,000
Total as a % of Loan Class	0.30%	0.41%
Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		$ 449,000,000
30-59
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		32,000,000
60-89
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		2,000,000
90+
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		4,000,000
Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		130,000,000
Unfunded loan commitment
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		76,000,000
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 424,000,000	$ 550,000,000
Total as a % of Loan Class	0.54%	0.70%
Commercial | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		$ 407,000,000
Commercial | 30-59
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		31,000,000
Commercial | 60-89
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Commercial | 90+
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Commercial | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		112,000,000
Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 125,000,000	$ 214,000,000
Total as a % of Loan Class	0.26%	0.45%
Weighted-Average Interest Rate Reduction	2.87%	3.06%
Weighted-Average Term Extension (in Months)	9 months	9 months
Weighted-Average Payment Deferral	$ 46,369	$ 471,296
Commercial | Commercial and industrial | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		151,000,000
Commercial | Commercial and industrial | 30-59
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		7,000,000
Commercial | Commercial and industrial | 60-89
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Commercial | Commercial and industrial | 90+
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Commercial | Commercial and industrial | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		56,000,000
Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 299,000,000	$ 336,000,000
Total as a % of Loan Class	1.03%	1.16%
Weighted-Average Interest Rate Reduction	0.00%	0.00%
Weighted-Average Term Extension (in Months)	7 months	8 months
Weighted-Average Payment Deferral	$ 10,229	$ 10,229
Commercial | Commercial real estate | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		256,000,000
Commercial | Commercial real estate | 30-59
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		24,000,000
Commercial | Commercial real estate | 60-89
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Commercial | Commercial real estate | 90+
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Commercial | Commercial real estate | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		56,000,000
Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 37,000,000	$ 67,000,000
Total as a % of Loan Class	0.05%	0.09%
Retail | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		$ 42,000,000
Retail | 30-59
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		1,000,000
Retail | 60-89
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		2,000,000
Retail | 90+
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		4,000,000
Retail | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		18,000,000
Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 27,000,000	$ 49,000,000
Total as a % of Loan Class	0.09%	0.16%
Weighted-Average Interest Rate Reduction	2.04%	1.86%
Weighted-Average Term Extension (in Months)	52 months	48 months
Weighted-Average Payment Deferral	$ 0	$ 0
Retail | Residential mortgages | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		33,000,000
Retail | Residential mortgages | 30-59
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Residential mortgages | 60-89
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		2,000,000
Retail | Residential mortgages | 90+
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		4,000,000
Retail | Residential mortgages | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		10,000,000
Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 4,000,000	$ 7,000,000
Total as a % of Loan Class	0.03%	0.05%
Weighted-Average Interest Rate Reduction	2.20%	2.12%
Weighted-Average Term Extension (in Months)	115 months	125 months
Weighted-Average Payment Deferral	$ 1,062	$ 1,917
Retail | Home equity | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		1,000,000
Retail | Home equity | 30-59
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Home equity | 60-89
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Home equity | 90+
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Home equity | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		6,000,000
Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 0	$ 0
Total as a % of Loan Class	0.00%	0.00%
Weighted-Average Interest Rate Reduction	2.40%	2.59%
Weighted-Average Term Extension (in Months)	19 months	21 months
Weighted-Average Payment Deferral	$ 1,342	$ 1,248
Retail | Automobile | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Automobile | 30-59
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Automobile | 60-89
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Automobile | 90+
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Automobile | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 3,000,000	$ 5,000,000
Total as a % of Loan Class	0.02%	0.04%
Weighted-Average Interest Rate Reduction	4.90%	5.00%
Weighted-Average Term Extension (in Months)	0 months	0 months
Weighted-Average Payment Deferral	$ 4,728	$ 3,610
Retail | Education | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		4,000,000
Retail | Education | 30-59
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Education | 60-89
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Education | 90+
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Education | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		1,000,000
Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 3,000,000	$ 6,000,000
Total as a % of Loan Class	0.06%	0.12%
Weighted-Average Interest Rate Reduction	18.76%	18.28%
Weighted-Average Term Extension (in Months)	0 months	22 months
Weighted-Average Payment Deferral	$ 0	$ 0
Retail | Other retail | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		4,000,000
Retail | Other retail | 30-59
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		1,000,000
Retail | Other retail | 60-89
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Other retail | 90+
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		0
Retail | Other retail | Nonaccrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis		1,000,000
Interest Rate Reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	7,000,000	14,000,000
Interest Rate Reduction | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Interest Rate Reduction | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Interest Rate Reduction | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Interest Rate Reduction | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	7,000,000	14,000,000
Interest Rate Reduction | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2,000,000	4,000,000
Interest Rate Reduction | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Interest Rate Reduction | Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Interest Rate Reduction | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2,000,000	4,000,000
Interest Rate Reduction | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	3,000,000	6,000,000
Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	440,000,000	533,000,000
Term Extension | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	421,000,000	495,000,000
Term Extension | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	123,000,000	160,000,000
Term Extension | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	298,000,000	335,000,000
Term Extension | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	19,000,000	38,000,000
Term Extension | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	17,000,000	35,000,000
Term Extension | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2,000,000	3,000,000
Term Extension | Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Term Extension | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Term Extension | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Payment Delay
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1,000,000	33,000,000
Payment Delay | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	32,000,000
Payment Delay | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	32,000,000
Payment Delay | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Payment Delay | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1,000,000	1,000,000
Payment Delay | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Payment Delay | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Payment Delay | Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Payment Delay | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1,000,000	1,000,000
Payment Delay | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Principal Forgiveness
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Principal Forgiveness | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Principal Forgiveness | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Amount of Principal Forgiven	0	0
Principal Forgiveness | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Amount of Principal Forgiven	0	0
Principal Forgiveness | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Principal Forgiveness | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Amount of Principal Forgiven	0	0
Principal Forgiveness | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Amount of Principal Forgiven	0	0
Principal Forgiveness | Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Amount of Principal Forgiven	0	0
Principal Forgiveness | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Amount of Principal Forgiven	0	0
Principal Forgiveness | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Amount of Principal Forgiven	1,000,000	2,000,000
Interest Rate Reduction and Term Extension
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	11,000,000	15,000,000
Interest Rate Reduction and Term Extension | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1,000,000	1,000,000
Interest Rate Reduction and Term Extension | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1,000,000	1,000,000
Interest Rate Reduction and Term Extension | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Interest Rate Reduction and Term Extension | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	10,000,000	14,000,000
Interest Rate Reduction and Term Extension | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	8,000,000	10,000,000
Interest Rate Reduction and Term Extension | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2,000,000	4,000,000
Interest Rate Reduction and Term Extension | Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Interest Rate Reduction and Term Extension | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Interest Rate Reduction and Term Extension | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Term Extension and Payment Delay
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2,000,000	22,000,000
Term Extension and Payment Delay | Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	2,000,000	22,000,000
Term Extension and Payment Delay | Commercial | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1,000,000	21,000,000
Term Extension and Payment Delay | Commercial | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	1,000,000	1,000,000
Term Extension and Payment Delay | Retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Term Extension and Payment Delay | Retail | Residential mortgages
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Term Extension and Payment Delay | Retail | Home equity
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Term Extension and Payment Delay | Retail | Automobile
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Term Extension and Payment Delay | Retail | Education
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	0	0
Term Extension and Payment Delay | Retail | Other retail
Financing Receivable, Troubled Debt Restructuring [Line Items]
Amortized cost basis	$ 0	$ 0