FAIR VALUE MEASUREMENTS - Unobservable Inputs Used and Valuation Techniques (Details) - Level 3	Sep. 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	0.1087
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	0.3732
Mortgage servicing rights | Maximum | Discounted Cash Flow | Option adjusted spread
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	10.6
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	0.1940
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	6.08
Asset-backed securities | Discounted Cash Flow | Conditional prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset-Backed Securities, measurement input	0.0800
Asset-backed securities | Discounted Cash Flow | Constant default rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Asset-Backed Securities, measurement input	0.0185
Other derivative contracts | Minimum | Internal Model | Pull through rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.1172
Other derivative contracts | Minimum | Internal Model | MSR value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.2673
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	1.2427
Other derivative contracts | Weighted Average | Internal Model | Pull through rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.8245
Other derivative contracts | Weighted Average | Internal Model | MSR value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other derivative contracts, measurement input	0.8138