BANK LOANS, NET, Held for Investment Residential Mortgage Loan Portfolio by FICO Score and by LTV Ratio (Details) - USD ($) $ in Millions	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	$ 25,314	$ 21,549	$ 21,109	$ 19,721	$ 17,197
Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	25,169	21,439	20,967	19,557	17,127
Residential mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	5,318	4,973
Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	5,318	4,973	$ 4,479	$ 3,775	$ 3,162
Below 80% | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	4,123	3,852
80%+ | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	1,195	1,121
Below 600 | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	67	67
600 - 699 | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	416	363
700 - 799 | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	3,772	3,463
800 + | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	1,058	1,076
FICO score not available | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable past due	$ 5	$ 4