BANK LOANS, NET, Held for Investment Residential Mortgage Loan Portfolio by FICO Score and by LTV Ratio (Details) - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held for investment	$ 44,098	$ 43,635
Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans held for investment	43,979	43,498
Residential mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	915	2,986
Fiscal year before current fiscal year	2,958	1,705
Fiscal year two years before current fiscal year	1,662	1,023
Fiscal year three years before current fiscal year	965	479
Fiscal year four years before current fiscal year	457	291
Prior	1,082	867
Revolving loans	40	35
Total loans held for investment	8,079	7,386
Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	915	2,986
Fiscal year before current fiscal year	2,958	1,705
Fiscal year two years before current fiscal year	1,662	1,023
Fiscal year three years before current fiscal year	965	479
Fiscal year four years before current fiscal year	457	291
Prior	1,082	867
Revolving loans	40	35
Total loans held for investment	8,079	7,386
Below 80% | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	639	2,287
Fiscal year before current fiscal year	2,262	1,333
Fiscal year two years before current fiscal year	1,300	797
Fiscal year three years before current fiscal year	755	358
Fiscal year four years before current fiscal year	341	226
Prior	832	661
Revolving loans	36	31
Total loans held for investment	6,165	5,693
80%+ | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	276	699
Fiscal year before current fiscal year	696	372
Fiscal year two years before current fiscal year	362	226
Fiscal year three years before current fiscal year	210	121
Fiscal year four years before current fiscal year	116	65
Prior	250	206
Revolving loans	4	4
Total loans held for investment	1,914	1,693
Below 600 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	6	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	70	64
600 - 699 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	51	155
Fiscal year before current fiscal year	155	112
Fiscal year two years before current fiscal year	107	90
Fiscal year three years before current fiscal year	88	32
Fiscal year four years before current fiscal year	31	20
Prior	83	68
Revolving loans	4	4
Total loans held for investment	519	481
700 - 799 | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	718	2,403
Fiscal year before current fiscal year	2,383	1,301
Fiscal year two years before current fiscal year	1,265	744
Fiscal year three years before current fiscal year	700	353
Fiscal year four years before current fiscal year	334	219
Prior	647	470
Revolving loans	25	22
Total loans held for investment	6,072	5,512
800 + | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	139	424
Fiscal year before current fiscal year	416	284
Fiscal year two years before current fiscal year	283	184
Fiscal year three years before current fiscal year	174	87
Fiscal year four years before current fiscal year	84	48
Prior	293	273
Revolving loans	8	6
Total loans held for investment	1,397	1,306
FICO score not available | Residential mortgage loans | Loans held for investment
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1	3
Fiscal year before current fiscal year	3	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	3	3
Total loans held for investment	$ 21	$ 23