BANK LOANS, NET, Credit Quality of Held for Investment Loan Portfolio (Details) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2024	Sep. 30, 2023
SBL
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	$ 76	$ 74
Fiscal year before current fiscal year	33	18
Fiscal year two years before current fiscal year	15	83
Fiscal year three years before current fiscal year	77	40
Fiscal year four years before current fiscal year	30	15
Prior	52	59
Revolving loans	15,146	14,317
Total loans held for investment	15,429	14,606
Gross charge-offs, current fiscal year	0
Gross charge-offs, fiscal year before current fiscal year	0
Gross charge-offs, fiscal year two years before current fiscal year	0
Gross charge-offs, fiscal year three years before current fiscal year	0
Gross charge-offs, fiscal year four years before current fiscal year	0
Gross charge-offs, prior	0
Gross charge-offs, revolving loans	0
Gross charge-offs, total	0
SBL | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	67	74
Fiscal year before current fiscal year	33	18
Fiscal year two years before current fiscal year	15	83
Fiscal year three years before current fiscal year	77	40
Fiscal year four years before current fiscal year	30	15
Prior	52	59
Revolving loans	15,146	14,293
Total loans held for investment	15,420	14,582
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	9	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	24
Total loans held for investment	9	24
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	470	672
Fiscal year before current fiscal year	586	1,153
Fiscal year two years before current fiscal year	1,089	1,120
Fiscal year three years before current fiscal year	758	1,096
Fiscal year four years before current fiscal year	679	1,037
Prior	3,418	2,743
Revolving loans	2,956	2,585
Total loans held for investment	9,956	10,406
Gross charge-offs, current fiscal year	0
Gross charge-offs, fiscal year before current fiscal year	0
Gross charge-offs, fiscal year two years before current fiscal year	0
Gross charge-offs, fiscal year three years before current fiscal year	3
Gross charge-offs, fiscal year four years before current fiscal year	4
Gross charge-offs, prior	30
Gross charge-offs, revolving loans	0
Gross charge-offs, total	37
C&I loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	470	672
Fiscal year before current fiscal year	586	1,148
Fiscal year two years before current fiscal year	1,084	1,091
Fiscal year three years before current fiscal year	758	965
Fiscal year four years before current fiscal year	602	1,020
Prior	3,383	2,675
Revolving loans	2,943	2,564
Total loans held for investment	9,826	10,135
C&I loans | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	5
Fiscal year two years before current fiscal year	5	29
Fiscal year three years before current fiscal year	0	69
Fiscal year four years before current fiscal year	38	0
Prior	15	0
Revolving loans	1	4
Total loans held for investment	59	107
C&I 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	62
Fiscal year four years before current fiscal year	39	17
Prior	20	65
Revolving loans	12	17
Total loans held for investment	71	161
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	0
Prior	0	3
Revolving loans	0	0
Total loans held for investment	0	3
CRE loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	682	1,137
Fiscal year before current fiscal year	1,235	2,344
Fiscal year two years before current fiscal year	2,246	1,120
Fiscal year three years before current fiscal year	982	812
Fiscal year four years before current fiscal year	737	621
Prior	1,329	967
Revolving loans	408	220
Total loans held for investment	7,619	7,221
Gross charge-offs, current fiscal year	0
Gross charge-offs, fiscal year before current fiscal year	0
Gross charge-offs, fiscal year two years before current fiscal year	0
Gross charge-offs, fiscal year three years before current fiscal year	0
Gross charge-offs, fiscal year four years before current fiscal year	0
Gross charge-offs, prior	8
Gross charge-offs, revolving loans	0
Gross charge-offs, total	8
CRE loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	682	1,130
Fiscal year before current fiscal year	1,176	2,344
Fiscal year two years before current fiscal year	2,210	1,115
Fiscal year three years before current fiscal year	977	766
Fiscal year four years before current fiscal year	690	604
Prior	1,205	845
Revolving loans	392	220
Total loans held for investment	7,332	7,024
CRE loans | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	7
Fiscal year before current fiscal year	59	0
Fiscal year two years before current fiscal year	27	0
Fiscal year three years before current fiscal year	0	14
Fiscal year four years before current fiscal year	38	5
Prior	20	55
Revolving loans	0	0
Total loans held for investment	144	81
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	9	5
Fiscal year three years before current fiscal year	5	32
Fiscal year four years before current fiscal year	9	12
Prior	96	67
Revolving loans	16	0
Total loans held for investment	135	116
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	8	0
Revolving loans	0	0
Total loans held for investment	8	0
REIT loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	145	258
Fiscal year before current fiscal year	244	200
Fiscal year two years before current fiscal year	182	214
Fiscal year three years before current fiscal year	216	101
Fiscal year four years before current fiscal year	95	172
Prior	263	176
Revolving loans	610	547
Total loans held for investment	1,755	1,668
Gross charge-offs, current fiscal year	0
Gross charge-offs, fiscal year before current fiscal year	0
Gross charge-offs, fiscal year two years before current fiscal year	0
Gross charge-offs, fiscal year three years before current fiscal year	0
Gross charge-offs, fiscal year four years before current fiscal year	0
Gross charge-offs, prior	0
Gross charge-offs, revolving loans	0
Gross charge-offs, total	0
REIT loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	145	258
Fiscal year before current fiscal year	232	200
Fiscal year two years before current fiscal year	182	214
Fiscal year three years before current fiscal year	216	101
Fiscal year four years before current fiscal year	95	172
Prior	250	176
Revolving loans	558	547
Total loans held for investment	1,678	1,668
REIT loans | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	12	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	13	0
Revolving loans	52	0
Total loans held for investment	77	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
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
Gross charge-offs, current fiscal year	0
Gross charge-offs, fiscal year before current fiscal year	0
Gross charge-offs, fiscal year two years before current fiscal year	0
Gross charge-offs, fiscal year three years before current fiscal year	0
Gross charge-offs, fiscal year four years before current fiscal year	0
Gross charge-offs, prior	0
Gross charge-offs, revolving loans	0
Gross charge-offs, total	0
Residential mortgage loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,028	1,765
Fiscal year before current fiscal year	1,678	2,889
Fiscal year two years before current fiscal year	2,784	1,607
Fiscal year three years before current fiscal year	1,525	919
Fiscal year four years before current fiscal year	874	433
Prior	1,304	992
Revolving loans	32	31
Total loans held for investment	9,225	8,636
Residential mortgage 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	1	2
Fiscal year three years before current fiscal year	0	0
Fiscal year four years before current fiscal year	0	2
Prior	5	5
Revolving loans	0	0
Total loans held for investment	6	9
Residential mortgage loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	2
Fiscal year two years before current fiscal year	3	0
Fiscal year three years before current fiscal year	0	1
Fiscal year four years before current fiscal year	0	0
Prior	11	14
Revolving loans	0	0
Total loans held for investment	14	17
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
Tax-exempt loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	62	147
Fiscal year before current fiscal year	57	279
Fiscal year two years before current fiscal year	266	161
Fiscal year three years before current fiscal year	153	54
Fiscal year four years before current fiscal year	54	97
Prior	839	803
Revolving loans	0	0
Total loans held for investment	1,431	1,541
Gross charge-offs, current fiscal year	0
Gross charge-offs, fiscal year before current fiscal year	0
Gross charge-offs, fiscal year two years before current fiscal year	0
Gross charge-offs, fiscal year three years before current fiscal year	0
Gross charge-offs, fiscal year four years before current fiscal year	0
Gross charge-offs, prior	0
Gross charge-offs, revolving loans	0
Gross charge-offs, total	0
Tax-exempt loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	62	147
Fiscal year before current fiscal year	57	279
Fiscal year two years before current fiscal year	266	161
Fiscal year three years before current fiscal year	153	54
Fiscal year four years before current fiscal year	54	97
Prior	839	803
Revolving loans	0	0
Total loans held for investment	1,431	1,541
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