BANK LOANS, NET, Held for Investment Residential Mortgage Loan Portfolio by FICO Score and by LTV Ratio (Details) - USD ($) $ in Millions	Mar. 31, 2022	Sep. 30, 2021
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	$ 28,211	$ 25,314
Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	27,932	25,169
Residential mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	5,945	5,318
Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	5,945	5,318
Below 80% | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	4,666	4,123
80%+ | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	1,279	1,195
Below 600 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	67	67
600 - 699 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	445	416
700 - 799 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	4,298	3,772
800 + | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	1,129	1,058
FICO score not available | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	$ 6	$ 5