BANK LOANS, NET, Analysis of Payment Status of Loans Held for Investment (Details) - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022
Financing Receivable, Past Due [Line Items]
Financing receivable past due	$ 44,098	$ 43,635
Performing nonaccrual loans	90	63
Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	43,979	43,498
Nonaccrual with allowance	66	44
Nonaccrual with no allowance	33	30
Total past due and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	4	4
30-89 days and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	4	4
90 days or more and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
Current and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	43,876	43,420
SBL
Financing Receivable, Past Due [Line Items]
Financing receivable past due	14,227	15,297
SBL | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	14,227	15,297
Nonaccrual with allowance	0	0
Nonaccrual with no allowance	0	0
SBL | Total past due and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
SBL | 30-89 days and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
SBL | 90 days or more and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
SBL | Current and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	14,227	15,297
C&I loans
Financing Receivable, Past Due [Line Items]
Financing receivable past due	11,259	11,173
Troubled debt restructuring	20	11
C&I loans | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	11,259	11,173
Nonaccrual with allowance	32	32
Nonaccrual with no allowance	0	0
C&I loans | Total past due and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
C&I loans | 30-89 days and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
C&I loans | 90 days or more and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
C&I loans | Current and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	11,227	11,141
CRE loans
Financing Receivable, Past Due [Line Items]
Financing receivable past due	7,054	6,549
Troubled debt restructuring	8	9
CRE loans | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	7,054	6,549
Nonaccrual with allowance	34	0
Nonaccrual with no allowance	18	16
CRE loans | Total past due and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
CRE loans | 30-89 days and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
CRE loans | 90 days or more and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
CRE loans | Current and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	7,002	6,521
REIT loans
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1,717	1,592
REIT loans | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1,717	1,592
Nonaccrual with allowance	0	12
Nonaccrual with no allowance	0	0
REIT loans | Total past due and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
REIT loans | 30-89 days and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
REIT loans | 90 days or more and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
REIT loans | Current and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1,717	1,592
Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1,643	1,501
Tax-exempt loans | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1,643	1,501
Nonaccrual with allowance	0	0
Nonaccrual with no allowance	0	0
Tax-exempt loans | Total past due and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
Tax-exempt loans | 30-89 days and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
Tax-exempt loans | 90 days or more and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
Tax-exempt loans | Current and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1,643	1,501
Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Financing receivable past due	8,079	7,386
Troubled debt restructuring	10	10
Residential mortgage loans | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	8,079	7,386
Nonaccrual with allowance	0	0
Nonaccrual with no allowance	15	14
Residential mortgage loans | Total past due and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	4	4
Residential mortgage loans | 30-89 days and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	4	4
Residential mortgage loans | 90 days or more and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
Residential mortgage loans | Current and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	$ 8,060	$ 7,368