FAIR VALUE MEASUREMENTS - Unobservable Inputs Used and Valuation Techniques (Details) - Level 3	Jun. 30, 2020
Mortgage servicing rights | Minimum | Discounted Cash Flow | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.1048
Mortgage servicing rights | Minimum | Discounted Cash Flow | Option adjusted spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	3.5
Mortgage servicing rights | Maximum | Discounted Cash Flow | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	0.3943
Mortgage servicing rights | Maximum | Discounted Cash Flow | Option adjusted spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	11.23
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	0.2100
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	6.21
Other derivative contracts | Minimum | Internal Model | Pull through rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.3206
Other derivative contracts | Minimum | Internal Model | MSR value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.572
Other derivative contracts | Maximum | Internal Model | Pull through rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	1.0000
Other derivative contracts | Maximum | Internal Model | MSR value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	1.3573
Other derivative contracts | Weighted Average | Internal Model | Pull through rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.7817
Other derivative contracts | Weighted Average | Internal Model | MSR value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.8878