BANK LOANS, NET, Credit Quality of Held for Investment Loan Portfolio (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
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	92	72
Fiscal year three years before current fiscal year	41	44
Fiscal year four years before current fiscal year	26	36
Prior	82	41
Revolving loans	13,948	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	92	72
Fiscal year three years before current fiscal year	41	44
Fiscal year four years before current fiscal year	26	36
Prior	82	41
Revolving loans	13,948	15,063
Total loans held for investment	14,227	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	0	0
Total loans held for investment	0	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	0	0
Total loans held for investment	0	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	454	1,022
Fiscal year before current fiscal year	1,203	1,476
Fiscal year two years before current fiscal year	1,283	1,364
Fiscal year three years before current fiscal year	1,301	1,189
Fiscal year four years before current fiscal year	1,115	1,434
Prior	3,357	2,288
Revolving loans	2,546	2,400
Total loans held for investment	11,259	11,173
C&I loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	454	1,011
Fiscal year before current fiscal year	1,193	1,448
Fiscal year two years before current fiscal year	1,254	1,301
Fiscal year three years before current fiscal year	1,223	1,124
Fiscal year four years before current fiscal year	1,097	1,389
Prior	3,272	2,200
Revolving loans	2,526	2,380
Total loans held for investment	11,019	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	38	37
Fiscal year four years before current fiscal year	0	0
Prior	1	82
Revolving loans	7	6
Total loans held for investment	85	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	40	28
Fiscal year four years before current fiscal year	18	40
Prior	84	6
Revolving loans	13	14
Total loans held for investment	155	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	620	1,916
Fiscal year before current fiscal year	2,346	1,346
Fiscal year two years before current fiscal year	1,195	906
Fiscal year three years before current fiscal year	822	724
Fiscal year four years before current fiscal year	667	898
Prior	1,255	583
Revolving loans	149	176
Total loans held for investment	7,054	6,549
CRE loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	613	1,916
Fiscal year before current fiscal year	2,346	1,345
Fiscal year two years before current fiscal year	1,195	892
Fiscal year three years before current fiscal year	784	707
Fiscal year four years before current fiscal year	654	816
Prior	1,180	551
Revolving loans	149	176
Total loans held for investment	6,921	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	0	0
Fiscal year three years before current fiscal year	36	0
Fiscal year four years before current fiscal year	0	36
Prior	22	2
Revolving loans	0	0
Total loans held for investment	65	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	13	46
Prior	53	30
Revolving loans	0	0
Total loans held for investment	68	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	266	169
Fiscal year before current fiscal year	202	230
Fiscal year two years before current fiscal year	214	96
Fiscal year three years before current fiscal year	101	53
Fiscal year four years before current fiscal year	55	40
Prior	197	222
Revolving loans	682	782
Total loans held for investment	1,717	1,592
REIT loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	266	169
Fiscal year before current fiscal year	202	230
Fiscal year two years before current fiscal year	214	96
Fiscal year three years before current fiscal year	101	53
Fiscal year four years before current fiscal year	55	40
Prior	197	222
Revolving loans	682	782
Total loans held for investment	1,717	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	165	264
Fiscal year before current fiscal year	298	169
Fiscal year two years before current fiscal year	165	56
Fiscal year three years before current fiscal year	56	115
Fiscal year four years before current fiscal year	108	192
Prior	851	705
Revolving loans	0	0
Total loans held for investment	1,643	1,501
Tax-exempt loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	165	264
Fiscal year before current fiscal year	298	169
Fiscal year two years before current fiscal year	165	56
Fiscal year three years before current fiscal year	56	115
Fiscal year four years before current fiscal year	108	192
Prior	851	705
Revolving loans	0	0
Total loans held for investment	1,643	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	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 | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	915	2,984
Fiscal year before current fiscal year	2,956	1,704
Fiscal year two years before current fiscal year	1,661	1,023
Fiscal year three years before current fiscal year	965	477
Fiscal year four years before current fiscal year	455	290
Prior	1,057	843
Revolving loans	40	35
Total loans held for investment	8,049	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	1	0
Fiscal year three years before current fiscal year	0	2
Fiscal year four years before current fiscal year	2	0
Prior	5	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	20	20
Revolving loans	0	0
Total loans held for investment	22	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