FAIR VALUE, Significant Assumptions Used in Valuation of Financial Instruments (Details) - Nonrecurring - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other assets: other real estate owned	$ 1	$ 1
Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other assets: other real estate owned	1	1
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other assets: other real estate owned	0	0
Impaired loans residential | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bank loans, net	17	21
Impaired loans residential | Level 2 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bank loans, net	4	7
Impaired loans residential | Level 3 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bank loans, net	$ 13	$ 14
Impaired loans residential | Level 3 | Discounted cash flow | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, prepayment rate (in years)	7 years	7 years
Impaired loans residential | Level 3 | Discounted cash flow | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, prepayment rate (in years)	12 years	12 years
Impaired loans residential | Level 3 | Discounted cash flow | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Debt securities, prepayment rate (in years)	10 years 7 months 6 days	10 years 4 months 24 days
Impaired loans corporate | Collateral or discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bank loans, net	$ 15	$ 21
Impaired loans corporate | Level 2 | Collateral or discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bank loans, net	0	0
Impaired loans corporate | Level 3 | Collateral or discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bank loans, net	15	21
Loans held for sale
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bank loans, net	38	66
Loans held for sale | Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bank loans, net	38	66
Loans held for sale | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bank loans, net	$ 0	$ 0