BANK LOANS, NET, Credit Quality of Held for Investment Loan Portfolio (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
SBL
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	20	14
Fiscal year before current fiscal year	18	27
Fiscal year two years before current fiscal year	83	72
Fiscal year three years before current fiscal year	44	44
Fiscal year four years before current fiscal year	16	36
Prior	38	41
Revolving loans	14,008	15,063
Total loans held for investment	14,227	15,297
SBL | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	20	14
Fiscal year before current fiscal year	18	27
Fiscal year two years before current fiscal year	83	72
Fiscal year three years before current fiscal year	44	44
Fiscal year four years before current fiscal year	16	36
Prior	38	41
Revolving loans	13,999	15,063
Total loans held for investment	14,218	15,297
SBL | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	0
Prior	0	0
Revolving loans	4	0
Total loans held for investment	4	0
SBL | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	0
Prior	0	0
Revolving loans	5	0
Total loans held for investment	5	0
SBL | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	0
Prior	0	0
Revolving loans	0	0
Total loans held for investment	0	0
C&I loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	551	1,022
Fiscal year before current fiscal year	1,152	1,476
Fiscal year two years before current fiscal year	1,144	1,364
Fiscal year three years before current fiscal year	1,170	1,189
Fiscal year four years before current fiscal year	992	1,434
Prior	2,986	2,288
Revolving loans	2,668	2,400
Total loans held for investment	10,663	11,173
C&I loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	551	1,011
Fiscal year before current fiscal year	1,142	1,448
Fiscal year two years before current fiscal year	1,115	1,301
Fiscal year three years before current fiscal year	1,109	1,124
Fiscal year four years before current fiscal year	974	1,389
Prior	2,904	2,200
Revolving loans	2,646	2,380
Total loans held for investment	10,441	10,853
C&I loans | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	10
Fiscal year before current fiscal year	10	28
Fiscal year two years before current fiscal year	29	3
Fiscal year three years before current fiscal year	0	37
Fiscal year four years before current fiscal year	0	0
Prior	19	82
Revolving loans	7	6
Total loans held for investment	65	166
C&I loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	1
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	60
Fiscal year three years before current fiscal year	61	28
Fiscal year four years before current fiscal year	18	40
Prior	63	6
Revolving loans	15	14
Total loans held for investment	157	149
C&I loans | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	5
Prior	0	0
Revolving loans	0	0
Total loans held for investment	0	5
CRE loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	783	1,916
Fiscal year before current fiscal year	2,356	1,346
Fiscal year two years before current fiscal year	1,156	906
Fiscal year three years before current fiscal year	823	724
Fiscal year four years before current fiscal year	630	898
Prior	1,134	583
Revolving loans	209	176
Total loans held for investment	7,091	6,549
CRE loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	776	1,916
Fiscal year before current fiscal year	2,356	1,345
Fiscal year two years before current fiscal year	1,151	892
Fiscal year three years before current fiscal year	787	707
Fiscal year four years before current fiscal year	618	816
Prior	1,040	551
Revolving loans	209	176
Total loans held for investment	6,937	6,403
CRE loans | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	7	0
Fiscal year before current fiscal year	0	1
Fiscal year two years before current fiscal year	5	0
Fiscal year three years before current fiscal year	34	0
Fiscal year four years before current fiscal year	0	36
Prior	22	2
Revolving loans	0	0
Total loans held for investment	68	39
CRE loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	14
Fiscal year three years before current fiscal year	2	17
Fiscal year four years before current fiscal year	12	46
Prior	72	30
Revolving loans	0	0
Total loans held for investment	86	107
CRE loans | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	0
Prior	0	0
Revolving loans	0	0
Total loans held for investment	0	0
REIT loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	279	169
Fiscal year before current fiscal year	201	230
Fiscal year two years before current fiscal year	211	96
Fiscal year three years before current fiscal year	103	53
Fiscal year four years before current fiscal year	55	40
Prior	175	222
Revolving loans	691	782
Total loans held for investment	1,715	1,592
REIT loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	279	169
Fiscal year before current fiscal year	201	230
Fiscal year two years before current fiscal year	211	96
Fiscal year three years before current fiscal year	103	53
Fiscal year four years before current fiscal year	55	40
Prior	175	222
Revolving loans	691	782
Total loans held for investment	1,715	1,592
REIT loans | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	0
Prior	0	0
Revolving loans	0	0
Total loans held for investment	0	0
REIT loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	0
Prior	0	0
Revolving loans	0	0
Total loans held for investment	0	0
REIT loans | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	0
Prior	0	0
Revolving loans	0	0
Total loans held for investment	0	0
Tax-exempt loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	90	264
Fiscal year before current fiscal year	297	169
Fiscal year two years before current fiscal year	162	56
Fiscal year three years before current fiscal year	56	115
Fiscal year four years before current fiscal year	100	192
Prior	843	705
Revolving loans	0	0
Total loans held for investment	1,548	1,501
Tax-exempt loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	90	264
Fiscal year before current fiscal year	297	169
Fiscal year two years before current fiscal year	162	56
Fiscal year three years before current fiscal year	56	115
Fiscal year four years before current fiscal year	100	192
Prior	843	705
Revolving loans	0	0
Total loans held for investment	1,548	1,501
Tax-exempt loans | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	0
Prior	0	0
Revolving loans	0	0
Total loans held for investment	0	0
Tax-exempt loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	0
Prior	0	0
Revolving loans	0	0
Total loans held for investment	0	0
Tax-exempt loans | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	0
Prior	0	0
Revolving loans	0	0
Total loans held for investment	0	0
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 | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,407	2,984
Fiscal year before current fiscal year	2,921	1,704
Fiscal year two years before current fiscal year	1,630	1,023
Fiscal year three years before current fiscal year	939	477
Fiscal year four years before current fiscal year	446	290
Prior	1,020	843
Revolving loans	33	35
Total loans held for investment	8,396	7,356
Residential mortgage loans | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	1
Fiscal year before current fiscal year	0	1
Fiscal year two years before current fiscal year	2	0
Fiscal year three years before current fiscal year	0	2
Fiscal year four years before current fiscal year	2	0
Prior	4	4
Revolving loans	0	0
Total loans held for investment	8	8
Residential mortgage loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	1
Fiscal year before current fiscal year	2	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	1
Prior	16	20
Revolving loans	0	0
Total loans held for investment	18	22
Residential mortgage loans | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	0
Prior	0	0
Revolving loans	0	0
Total loans held for investment	$ 0	$ 0