BANK LOANS, NET, Credit Quality of Held for Investment Loan Portfolio (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Sep. 30, 2023
SBL
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	$ 50	$ 74
Fiscal year before current fiscal year	47	18
Fiscal year two years before current fiscal year	19	83
Fiscal year three years before current fiscal year	82	40
Fiscal year four years before current fiscal year	36	15
Prior	74	59
Revolving loans	14,339	14,317
Total loans held for investment	14,647	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	31	74
Fiscal year before current fiscal year	47	18
Fiscal year two years before current fiscal year	19	83
Fiscal year three years before current fiscal year	82	40
Fiscal year four years before current fiscal year	36	15
Prior	74	59
Revolving loans	14,339	14,293
Total loans held for investment	14,628	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	19	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	19	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	138	672
Fiscal year before current fiscal year	732	1,153
Fiscal year two years before current fiscal year	1,211	1,120
Fiscal year three years before current fiscal year	1,096	1,096
Fiscal year four years before current fiscal year	1,007	1,037
Prior	3,516	2,743
Revolving loans	2,803	2,585
Total loans held for investment	10,503	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	1
Gross charge-offs, fiscal year four years before current fiscal year	0
Gross charge-offs, prior	5
Gross charge-offs, revolving loans	0
Gross charge-offs, total	6
C&I loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	138	672
Fiscal year before current fiscal year	732	1,148
Fiscal year two years before current fiscal year	1,206	1,091
Fiscal year three years before current fiscal year	1,067	965
Fiscal year four years before current fiscal year	877	1,020
Prior	3,457	2,675
Revolving loans	2,784	2,564
Total loans held for investment	10,261	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	68	0
Prior	0	0
Revolving loans	3	4
Total loans held for investment	76	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	29	62
Fiscal year four years before current fiscal year	62	17
Prior	59	65
Revolving loans	16	17
Total loans held for investment	166	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	131	1,137
Fiscal year before current fiscal year	1,188	2,344
Fiscal year two years before current fiscal year	2,317	1,120
Fiscal year three years before current fiscal year	1,112	812
Fiscal year four years before current fiscal year	785	621
Prior	1,543	967
Revolving loans	255	220
Total loans held for investment	7,331	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	2
Gross charge-offs, revolving loans	0
Gross charge-offs, total	2
CRE loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	131	1,130
Fiscal year before current fiscal year	1,182	2,344
Fiscal year two years before current fiscal year	2,317	1,115
Fiscal year three years before current fiscal year	1,107	766
Fiscal year four years before current fiscal year	739	604
Prior	1,411	845
Revolving loans	255	220
Total loans held for investment	7,142	7,024
CRE loans | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	7
Fiscal year before current fiscal year	6	0
Fiscal year two years before current fiscal year	0	0
Fiscal year three years before current fiscal year	0	14
Fiscal year four years before current fiscal year	14	5
Prior	19	55
Revolving loans	0	0
Total loans held for investment	39	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	0	5
Fiscal year three years before current fiscal year	5	32
Fiscal year four years before current fiscal year	32	12
Prior	113	67
Revolving loans	0	0
Total loans held for investment	150	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	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	51	258
Fiscal year before current fiscal year	236	200
Fiscal year two years before current fiscal year	184	214
Fiscal year three years before current fiscal year	232	101
Fiscal year four years before current fiscal year	103	172
Prior	311	176
Revolving loans	580	547
Total loans held for investment	1,697	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	51	258
Fiscal year before current fiscal year	236	200
Fiscal year two years before current fiscal year	184	214
Fiscal year three years before current fiscal year	232	101
Fiscal year four years before current fiscal year	103	172
Prior	311	176
Revolving loans	580	547
Total loans held for investment	1,697	1,668
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
Residential mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	323	1,765
Fiscal year before current fiscal year	1,747	2,891
Fiscal year two years before current fiscal year	2,861	1,609
Fiscal year three years before current fiscal year	1,588	920
Fiscal year four years before current fiscal year	903	435
Prior	1,406	1,011
Revolving loans	33	31
Total loans held for investment	8,861	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	323	1,765
Fiscal year before current fiscal year	1,747	2,889
Fiscal year two years before current fiscal year	2,857	1,607
Fiscal year three years before current fiscal year	1,588	919
Fiscal year four years before current fiscal year	903	433
Prior	1,388	992
Revolving loans	33	31
Total loans held for investment	8,839	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	2	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	7	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	2	0
Fiscal year three years before current fiscal year	0	1
Fiscal year four years before current fiscal year	0	0
Prior	13	14
Revolving loans	0	0
Total loans held for investment	15	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	0	147
Fiscal year before current fiscal year	57	279
Fiscal year two years before current fiscal year	270	161
Fiscal year three years before current fiscal year	160	54
Fiscal year four years before current fiscal year	54	97
Prior	870	803
Revolving loans	0	0
Total loans held for investment	1,411	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	0	147
Fiscal year before current fiscal year	57	279
Fiscal year two years before current fiscal year	270	161
Fiscal year three years before current fiscal year	160	54
Fiscal year four years before current fiscal year	54	97
Prior	870	803
Revolving loans	0	0
Total loans held for investment	1,411	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