BANK LOANS, NET, Held for Investment Residential Mortgage Loan Portfolio by FICO Score and by LTV Ratio (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023
Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held for investment	$ 46,267	$ 44,104
Residential mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,373	1,765
Fiscal year before current fiscal year	1,637	2,891
Fiscal year two years before current fiscal year	2,734	1,609
Fiscal year three years before current fiscal year	1,494	920
Fiscal year four years before current fiscal year	858	435
Prior	1,277	1,011
Revolving loans	39	31
Total loans held for investment	9,412	8,662
Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,373	1,765
Fiscal year before current fiscal year	1,637	2,891
Fiscal year two years before current fiscal year	2,734	1,609
Fiscal year three years before current fiscal year	1,494	920
Fiscal year four years before current fiscal year	858	435
Prior	1,277	1,011
Revolving loans	39	31
Total loans held for investment	9,412	8,662
Below 80% | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	988	1,244
Fiscal year before current fiscal year	1,155	2,218
Fiscal year two years before current fiscal year	2,104	1,257
Fiscal year three years before current fiscal year	1,182	716
Fiscal year four years before current fiscal year	665	323
Prior	973	780
Revolving loans	38	29
Total loans held for investment	7,105	6,567
80%+ | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	385	521
Fiscal year before current fiscal year	482	673
Fiscal year two years before current fiscal year	630	352
Fiscal year three years before current fiscal year	312	204
Fiscal year four years before current fiscal year	193	112
Prior	304	231
Revolving loans	1	2
Total loans held for investment	2,307	2,095
Below 600 | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1	7
Fiscal year before current fiscal year	7	1
Fiscal year two years before current fiscal year	13	3
Fiscal year three years before current fiscal year	5	2
Fiscal year four years before current fiscal year	3	3
Prior	14	55
Revolving loans	0	0
Total loans held for investment	43	71
600 - 699 | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	79	99
Fiscal year before current fiscal year	52	154
Fiscal year two years before current fiscal year	107	106
Fiscal year three years before current fiscal year	52	83
Fiscal year four years before current fiscal year	44	30
Prior	124	79
Revolving loans	5	4
Total loans held for investment	463	555
700 - 799 | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,093	1,381
Fiscal year before current fiscal year	992	2,327
Fiscal year two years before current fiscal year	1,564	1,218
Fiscal year three years before current fiscal year	793	666
Fiscal year four years before current fiscal year	469	320
Prior	636	609
Revolving loans	23	20
Total loans held for investment	5,570	6,541
800 + | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	197	274
Fiscal year before current fiscal year	584	407
Fiscal year two years before current fiscal year	1,050	279
Fiscal year three years before current fiscal year	642	168
Fiscal year four years before current fiscal year	341	77
Prior	499	265
Revolving loans	10	6
Total loans held for investment	3,323	1,476
FICO score not available | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	3	4
Fiscal year before current fiscal year	2	2
Fiscal year two years before current fiscal year	0	3
Fiscal year three years before current fiscal year	2	1
Fiscal year four years before current fiscal year	1	5
Prior	4	3
Revolving loans	1	1
Total loans held for investment	$ 13	$ 19