FAIR VALUE MEASUREMENTS - Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities available for sale	$ 3,177	$ 3,275
Debt securities held to maturity	3,587	3,687
Net loans and leases, including loans held for sale	34	12
Derivative assets	103	96
Long-term borrowings	630
Derivative liabilities	388	411
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,704	1,674
Debt securities available for sale	306	257
Debt securities held to maturity	0	0
Net loans and leases, including loans held for sale	0	0
Loan servicing rights	0	0
Derivative assets	0	0
Accrued interest receivable	137	126
Deposits	28,490	31,158
Short-term borrowings	2,390	1,369
Long-term borrowings	0	0
Derivative liabilities	0	0
Accrued interest payable	55	31
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Debt securities available for sale	2,871	3,018
Debt securities held to maturity	3,587	3,687
Net loans and leases, including loans held for sale	82	91
Loan servicing rights	0	0
Derivative assets	103	96
Accrued interest receivable	0	0
Deposits	5,247	3,515
Short-term borrowings	0	0
Long-term borrowings	1,190	0
Derivative liabilities	386	399
Accrued interest payable	0	0
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Debt securities available for sale	0	0
Debt securities held to maturity	0	0
Net loans and leases, including loans held for sale	30,164	28,917
Loan servicing rights	74	71
Derivative assets	0	0
Accrued interest receivable	0	0
Deposits	0	0
Short-term borrowings	0	0
Long-term borrowings	736	1,061
Derivative liabilities	2	12
Accrued interest payable	0	0
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,704	1,674
Debt securities available for sale	3,177	3,275
Debt securities held to maturity	3,988	4,087
Net loans and leases, including loans held for sale	31,035	29,977
Loan servicing rights	58	55
Derivative assets	103	96
Accrued interest receivable	137	126
Deposits	33,825	34,770
Short-term borrowings	2,391	1,372
Long-term borrowings	1,981	1,093
Derivative liabilities	388	411
Accrued interest payable	55	31
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,704	1,674
Debt securities available for sale	3,177	3,275
Debt securities held to maturity	3,587	3,687
Net loans and leases, including loans held for sale	30,246	29,008
Loan servicing rights	74	71
Derivative assets	103	96
Accrued interest receivable	137	126
Deposits	33,737	34,673
Short-term borrowings	2,390	1,369
Long-term borrowings	1,926	1,061
Derivative liabilities	388	411
Accrued interest payable	$ 55	$ 31