BANK LOANS, NET, Held for Investment Residential Mortgage Loan Portfolio by FICO Score and by LTV Ratio (Details) - USD ($) $ in Millions	Jun. 30, 2024	Sep. 30, 2023
Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held for investment	$ 45,435	$ 44,104
Residential mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,028	1,765
Fiscal year before current fiscal year	1,678	2,891
Fiscal year two years before current fiscal year	2,788	1,609
Fiscal year three years before current fiscal year	1,525	920
Fiscal year four years before current fiscal year	874	435
Prior	1,320	1,011
Revolving loans	32	31
Total loans held for investment	9,245	8,662
Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,028	1,765
Fiscal year before current fiscal year	1,678	2,891
Fiscal year two years before current fiscal year	2,788	1,609
Fiscal year three years before current fiscal year	1,525	920
Fiscal year four years before current fiscal year	874	435
Prior	1,320	1,011
Revolving loans	32	31
Total loans held for investment	9,245	8,662
Below 80% | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	757	1,244
Fiscal year before current fiscal year	1,185	2,218
Fiscal year two years before current fiscal year	2,144	1,257
Fiscal year three years before current fiscal year	1,201	716
Fiscal year four years before current fiscal year	677	323
Prior	1,006	780
Revolving loans	31	29
Total loans held for investment	7,001	6,567
80%+ | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	271	521
Fiscal year before current fiscal year	493	673
Fiscal year two years before current fiscal year	644	352
Fiscal year three years before current fiscal year	324	204
Fiscal year four years before current fiscal year	197	112
Prior	314	231
Revolving loans	1	2
Total loans held for investment	2,244	2,095
Below 600 | Residential mortgage loans | 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	15	55
Revolving loans	0	0
Total loans held for investment	44	71
600 - 699 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	43	99
Fiscal year before current fiscal year	53	154
Fiscal year two years before current fiscal year	111	106
Fiscal year three years before current fiscal year	52	83
Fiscal year four years before current fiscal year	45	30
Prior	129	79
Revolving loans	3	4
Total loans held for investment	436	555
700 - 799 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	838	1,381
Fiscal year before current fiscal year	1,012	2,327
Fiscal year two years before current fiscal year	1,599	1,218
Fiscal year three years before current fiscal year	806	666
Fiscal year four years before current fiscal year	480	320
Prior	652	609
Revolving loans	19	20
Total loans held for investment	5,406	6,541
800 + | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	145	274
Fiscal year before current fiscal year	602	407
Fiscal year two years before current fiscal year	1,065	279
Fiscal year three years before current fiscal year	660	168
Fiscal year four years before current fiscal year	345	77
Prior	520	265
Revolving loans	9	6
Total loans held for investment	3,346	1,476
FICO score not available | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1	4
Fiscal year before current fiscal year	4	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