FAIR VALUE MEASUREMENTS - Schedule of Non-Recurring Basis Assets (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	$ 75.2	$ 71.8	$ 67.8	$ 68.6
Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans	29.0	35.0
Indirect installment loans held for sale		338.0
Other real estate owned		2.0
Fair Value, Nonrecurring | Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	1.0	12.0
Fair Value, Nonrecurring | SBA-Guaranteed Loan Servicing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets		1.0
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0.0	0.0
Level 1 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans	0.0	0.0
Indirect installment loans held for sale		0.0
Other real estate owned		0.0
Level 1 | Fair Value, Nonrecurring | Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0.0	0.0
Level 1 | Fair Value, Nonrecurring | SBA-Guaranteed Loan Servicing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets		0.0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0.0	0.0
Level 2 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans	0.0	0.0
Indirect installment loans held for sale		0.0
Other real estate owned		0.0
Level 2 | Fair Value, Nonrecurring | Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0.0	0.0
Level 2 | Fair Value, Nonrecurring | SBA-Guaranteed Loan Servicing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets		0.0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	77.0	73.0
Level 3 | Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Collateral dependent loans	29.0	35.0
Indirect installment loans held for sale		338.0
Other real estate owned		2.0
Level 3 | Fair Value, Nonrecurring | Mortgage Servicing Rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	$ 1.0	12.0
Level 3 | Fair Value, Nonrecurring | SBA-Guaranteed Loan Servicing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets		$ 1.0