BANK LOANS, NET, Held for Investment Residential Mortgage Loan Portfolio by LTV Ratio and FICO Score (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held for investment	$ 51,603	$ 46,267
Residential mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,810	1,373
Fiscal year before current fiscal year	1,206	1,637
Fiscal year two years before current fiscal year	1,465	2,734
Fiscal year three years before current fiscal year	2,518	1,494
Fiscal year four years before current fiscal year	1,390	858
Prior	1,864	1,277
Revolving loans	42	39
Total loans held for investment	10,295	9,412
Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,810	1,373
Fiscal year before current fiscal year	1,206	1,637
Fiscal year two years before current fiscal year	1,465	2,734
Fiscal year three years before current fiscal year	2,518	1,494
Fiscal year four years before current fiscal year	1,390	858
Prior	1,864	1,277
Revolving loans	42	39
Total loans held for investment	10,295	9,412
Below 80% | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,271	988
Fiscal year before current fiscal year	874	1,155
Fiscal year two years before current fiscal year	1,037	2,104
Fiscal year three years before current fiscal year	1,926	1,182
Fiscal year four years before current fiscal year	1,100	665
Prior	1,432	973
Revolving loans	41	38
Total loans held for investment	7,681	7,105
80%+ | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	539	385
Fiscal year before current fiscal year	332	482
Fiscal year two years before current fiscal year	428	630
Fiscal year three years before current fiscal year	592	312
Fiscal year four years before current fiscal year	290	193
Prior	432	304
Revolving loans	1	1
Total loans held for investment	2,614	2,307
Below 600 | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	5	1
Fiscal year before current fiscal year	5	7
Fiscal year two years before current fiscal year	11	13
Fiscal year three years before current fiscal year	17	5
Fiscal year four years before current fiscal year	7	3
Prior	18	14
Revolving loans	0	0
Total loans held for investment	63	43
600 - 699 | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	74	79
Fiscal year before current fiscal year	60	52
Fiscal year two years before current fiscal year	66	107
Fiscal year three years before current fiscal year	96	52
Fiscal year four years before current fiscal year	43	44
Prior	90	124
Revolving loans	5	5
Total loans held for investment	434	463
700 - 799 | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,424	1,093
Fiscal year before current fiscal year	747	992
Fiscal year two years before current fiscal year	815	1,564
Fiscal year three years before current fiscal year	1,419	793
Fiscal year four years before current fiscal year	744	469
Prior	1,026	636
Revolving loans	29	23
Total loans held for investment	6,204	5,570
800 + | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	306	197
Fiscal year before current fiscal year	392	584
Fiscal year two years before current fiscal year	572	1,050
Fiscal year three years before current fiscal year	986	642
Fiscal year four years before current fiscal year	594	341
Prior	727	499
Revolving loans	8	10
Total loans held for investment	3,585	3,323
FICO score not available | Residential mortgage loans | Total loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1	3
Fiscal year before current fiscal year	2	2
Fiscal year two years before current fiscal year	1	0
Fiscal year three years before current fiscal year	0	2
Fiscal year four years before current fiscal year	2	1
Prior	3	4
Revolving loans	0	1
Total loans held for investment	$ 9	$ 13