BANK LOANS, NET, Collateral-dependent loans (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	$ 1	$ 0
CRE loans | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	0	0
CRE loans | Retail and Industrial Real Estate | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Collateral dependent loans	13
Residential mortgage loans | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	1	0
Residential mortgage loans | One-to-four family residential mortgage loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	6	$ 6
Residential mortgage loans | Single Family | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Collateral dependent loans	$ 6