FAIR VALUE MEASUREMENTS - Summary of information about significant unobservable inputs (Level 3) used in the valuation of MSRs measured at fair value on a recurring basis (Level 3) (Details)	Sep. 30, 2021	Sep. 30, 2020
Discount rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input		9.25
Discount rate | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	8.50
Discount rate | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	10.00
Discount rate | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	8.51
Prepayment rate | Minimum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	6.04	2.99
Prepayment rate | Maximum [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	43.27	86.98
Prepayment rate | Weighted Average [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Mortgage servicing rights, measurement input	10.00	18.08