BANK LOANS, NET, Collateral-dependent loans (Details) - USD ($) $ in Millions	Jun. 30, 2022	Sep. 30, 2021
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	$ 42,220	$ 25,314
Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	42,054	25,169
C&I loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	10,897	8,440
C&I loans | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	10,897	8,440
C&I loans | Retail, industrial and healthcare | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Collateral dependent loans	13
CRE loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	6,354	2,872
CRE loans | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	6,354	2,872
CRE loans | Retail, industrial and healthcare | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Collateral dependent loans	28	20
Residential mortgage loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	6,728	5,318
Residential mortgage loans | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	6,728	5,318
Residential mortgage loans | One-to-four family residential mortgage loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable past due	5	4
Residential mortgage loans | Single family | Loans held for investment
Financing Receivable, Allowance for Credit Loss [Line Items]
Collateral dependent loans	$ 7	$ 5