BANK LOANS, NET, Collateral-dependent loans (Details) - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	$ 44,098	$ 43,635
Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	43,979	43,498
C&I loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	11,259	11,173
C&I loans | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	11,259	11,173
C&I loans | Commercial real estate and other business assets | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, gross	9	11
CRE loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	7,054	6,549
CRE loans | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	7,054	6,549
CRE loans | Retail, industrial, office and health care real estate | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, gross	52	21
Residential mortgage loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	8,079	7,386
Residential mortgage loans | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	8,079	7,386
Residential mortgage loans | One-to-four family residential mortgage loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	5	5
Residential mortgage loans | Single family homes | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, gross	$ 6	$ 6