FAIR VALUE, Financial Instruments Measured at Fair Value on a Nonrecurring Basis (Details) - Nonrecurring - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Other assets: other real estate owned			$ 1
Level 2
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Other assets: other real estate owned			1
Level 3
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Other assets: other real estate owned			0
Loans held for sale
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Bank loans, net	$ 104		38
Loans held for sale | Level 2
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Bank loans, net	104		38
Loans held for sale | Level 3
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Bank loans, net	0		0
Discounted cash flow | Bank loans: impaired loans - residential
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Bank loans, net	16		17
Discounted cash flow | Bank loans: impaired loans - residential | Level 2
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Bank loans, net	4		4
Discounted cash flow | Bank loans: impaired loans - residential | Level 3
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Bank loans, net	12		13
Collateral or discounted cash flow | Bank loans: impaired loans - corporate
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Bank loans, net	14		15
Collateral or discounted cash flow | Bank loans: impaired loans - corporate | Level 2
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Bank loans, net	0		0
Collateral or discounted cash flow | Bank loans: impaired loans - corporate | Level 3
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Bank loans, net	$ 14		$ 15
Minimum | Discounted cash flow | Bank loans: impaired loans - residential | Level 3
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Prepayment term	7 years	7 years
Maximum | Discounted cash flow | Bank loans: impaired loans - residential | Level 3
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Prepayment term	12 years	12 years
Weighted average | Discounted cash flow | Bank loans: impaired loans - residential | Level 3
Fair Value, Assets and Liabilities Measured on Nonrecurring Basis [Line Items]
Prepayment term	10 years 7 months 6 days	10 years 7 months 6 days