BANK LOANS, NET, Analysis of Payment Status of Loans Held for Investment (Details) - USD ($) $ in Millions	Jun. 30, 2022	Sep. 30, 2021
Financing Receivable, Past Due [Line Items]
Financing receivable past due	$ 42,220	$ 25,314
Performing nonaccrual loans	78	61
Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	42,054	25,169
Nonaccrual with allowance	59	41
Nonaccrual with no allowance	31	33
Total past due and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	18	2
30-89 days and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	18	2
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	41,946	25,093
C&I loans
Financing Receivable, Past Due [Line Items]
Financing receivable past due	10,897	8,440
Troubled debt restructuring	13
C&I loans | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	10,897	8,440
Nonaccrual with allowance	46	39
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	16	0
C&I loans | 30-89 days and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	16	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	10,835	8,401
CRE loans
Financing Receivable, Past Due [Line Items]
Financing receivable past due	6,354	2,872
Troubled debt restructuring	9	12
CRE loans | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	6,354	2,872
Nonaccrual with allowance	12	0
Nonaccrual with no allowance	17	20
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	6,325	2,852
REIT loans
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1,416	1,112
REIT loans | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1,416	1,112
Nonaccrual with allowance	0	0
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	1,416	1,112
Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1,347	1,321
Tax-exempt loans | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1,347	1,321
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	1,347	1,321
Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Financing receivable past due	6,728	5,318
Troubled debt restructuring	11	13
Residential mortgage loans | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	6,728	5,318
Nonaccrual with allowance	1	2
Nonaccrual with no allowance	14	13
Residential mortgage loans | Total past due and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1	2
Residential mortgage loans | 30-89 days and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1	2
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	6,712	5,301
SBL and other
Financing Receivable, Past Due [Line Items]
Financing receivable past due	15,312	6,106
SBL and other | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	15,312	6,106
Nonaccrual with allowance	0	0
Nonaccrual with no allowance	0	0
SBL and other | Total past due and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1	0
SBL and other | 30-89 days and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	1	0
SBL and other | 90 days or more and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	0	0
SBL and other | Current and accruing | Loans held for investment
Financing Receivable, Past Due [Line Items]
Financing receivable past due	$ 15,311	$ 6,106