BANK LOANS, NET, Held for Investment Residential Mortgage Loan Portfolio by FICO Score and by LTV Ratio (Details) - USD ($) $ in Millions	Jun. 30, 2023	Sep. 30, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held for investment	$ 43,801	$ 43,635
Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held for investment	43,666	43,498
Residential mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,407	2,986
Fiscal year before current fiscal year	2,923	1,705
Fiscal year two years before current fiscal year	1,632	1,023
Fiscal year three years before current fiscal year	939	479
Fiscal year four years before current fiscal year	448	291
Prior	1,040	867
Revolving loans	33	35
Total loans held for investment	8,422	7,386
Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,407	2,986
Fiscal year before current fiscal year	2,923	1,705
Fiscal year two years before current fiscal year	1,632	1,023
Fiscal year three years before current fiscal year	939	479
Fiscal year four years before current fiscal year	448	291
Prior	1,040	867
Revolving loans	33	35
Total loans held for investment	8,422	7,386
Below 80% | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	974	2,287
Fiscal year before current fiscal year	2,243	1,333
Fiscal year two years before current fiscal year	1,276	797
Fiscal year three years before current fiscal year	732	358
Fiscal year four years before current fiscal year	334	226
Prior	801	661
Revolving loans	31	31
Total loans held for investment	6,391	5,693
80%+ | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	433	699
Fiscal year before current fiscal year	680	372
Fiscal year two years before current fiscal year	356	226
Fiscal year three years before current fiscal year	207	121
Fiscal year four years before current fiscal year	114	65
Prior	239	206
Revolving loans	2	4
Total loans held for investment	2,031	1,693
Below 600 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	7	1
Fiscal year before current fiscal year	1	3
Fiscal year two years before current fiscal year	3	2
Fiscal year three years before current fiscal year	2	3
Fiscal year four years before current fiscal year	3	1
Prior	55	54
Revolving loans	0	0
Total loans held for investment	71	64
600 - 699 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	79	155
Fiscal year before current fiscal year	155	112
Fiscal year two years before current fiscal year	106	90
Fiscal year three years before current fiscal year	85	32
Fiscal year four years before current fiscal year	30	20
Prior	80	68
Revolving loans	3	4
Total loans held for investment	538	481
700 - 799 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,110	2,403
Fiscal year before current fiscal year	2,353	1,301
Fiscal year two years before current fiscal year	1,239	744
Fiscal year three years before current fiscal year	681	353
Fiscal year four years before current fiscal year	327	219
Prior	624	470
Revolving loans	23	22
Total loans held for investment	6,357	5,512
800 + | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	209	424
Fiscal year before current fiscal year	412	284
Fiscal year two years before current fiscal year	280	184
Fiscal year three years before current fiscal year	170	87
Fiscal year four years before current fiscal year	83	48
Prior	277	273
Revolving loans	6	6
Total loans held for investment	1,437	1,306
FICO score not available | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	2	3
Fiscal year before current fiscal year	2	5
Fiscal year two years before current fiscal year	4	3
Fiscal year three years before current fiscal year	1	4
Fiscal year four years before current fiscal year	5	3
Prior	4	2
Revolving loans	1	3
Total loans held for investment	$ 19	$ 23