BANK LOANS, NET, Held for Investment Residential Mortgage Loan Portfolio by FICO Score and by LTV Ratio (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, gross	$ 22,335	$ 21,549
Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, gross	22,126	21,439
Residential mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, gross	4,928
Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, gross	4,928	4,973
Below 80% | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, gross	3,812	3,852
80%+ | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, gross	1,116	1,121
Below 600 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, gross	67	67
600 - 699 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, gross	380	363
700 - 799 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, gross	3,424	3,463
800 + | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, gross	1,052	1,076
FICO score not available | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, gross	$ 5	$ 4