FAIR VALUE MEASUREMENTS - Unobservable Inputs Used and Valuation Techniques (Details) - Level 3	Jun. 30, 2021
Mortgage servicing rights | Minimum | Discounted Cash Flow | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.1056
Mortgage servicing rights | Minimum | Discounted Cash Flow | Option adjusted spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	(14.90)
Mortgage servicing rights | Maximum | Discounted Cash Flow | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.2954
Mortgage servicing rights | Maximum | Discounted Cash Flow | Option adjusted spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	10.60
Mortgage servicing rights | Weighted Average | Discounted Cash Flow | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.119
Mortgage servicing rights | Weighted Average | Discounted Cash Flow | Option adjusted spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	5.81
Customer commodity contracts | Minimum | Internal Model | Pull through rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.1038
Customer commodity contracts | Minimum | Internal Model | MSR value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	(0.0021)
Customer commodity contracts | Maximum | Internal Model | Pull through rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.9990
Customer commodity contracts | Maximum | Internal Model | MSR value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	1.5476
Customer commodity contracts | Weighted Average | Internal Model | Pull through rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.8166
Customer commodity contracts | Weighted Average | Internal Model | MSR value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.9901