BANK LOANS, NET, Information on Delinquency Status of Loans Held for Investment (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Financing Receivable, Past Due [Line Items]
Performing nonaccrual loans	$ 109	$ 89
SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	19,775	16,233
C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	10,777	9,953
CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	7,840	7,615
REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,690	1,716
Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	10,295	9,412
Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,226	1,338
Total loans held for investment
Financing Receivable, Past Due [Line Items]
Total loans held for investment	51,603	46,267
Nonaccrual with allowance	159	144
Nonaccrual with no allowance	27	31
Total loans held for investment | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	19,775	16,233
Nonaccrual with allowance	0	0
Nonaccrual with no allowance	0	0
Total loans held for investment | C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	10,777	9,953
Nonaccrual with allowance	39	58
Nonaccrual with no allowance	5	0
Total loans held for investment | CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	7,840	7,615
Nonaccrual with allowance	101	67
Nonaccrual with no allowance	9	18
Total loans held for investment | REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,690	1,716
Nonaccrual with allowance	19	19
Nonaccrual with no allowance	0	0
Total loans held for investment | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	10,295	9,412
Nonaccrual with allowance	0	0
Nonaccrual with no allowance	13	13
Total loans held for investment | Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,226	1,338
Nonaccrual with allowance	0	0
Nonaccrual with no allowance	0	0
Total loans held for investment | Total past due and accruing
Financing Receivable, Past Due [Line Items]
Total loans held for investment	7	6
Total loans held for investment | Total past due and accruing | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1	3
Total loans held for investment | Total past due and accruing | C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1	0
Total loans held for investment | Total past due and accruing | CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | Total past due and accruing | REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | Total past due and accruing | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	5	3
Total loans held for investment | Total past due and accruing | Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | 30-89 days and accruing
Financing Receivable, Past Due [Line Items]
Total loans held for investment	7	6
Total loans held for investment | 30-89 days and accruing | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1	3
Total loans held for investment | 30-89 days and accruing | C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1	0
Total loans held for investment | 30-89 days and accruing | CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | 30-89 days and accruing | REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | 30-89 days and accruing | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	5	3
Total loans held for investment | 30-89 days and accruing | Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | 90 days or more and accruing
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | 90 days or more and accruing | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | 90 days or more and accruing | C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | 90 days or more and accruing | CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | 90 days or more and accruing | REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | 90 days or more and accruing | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | 90 days or more and accruing | Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
Total loans held for investment | Current and accruing
Financing Receivable, Past Due [Line Items]
Total loans held for investment	51,410	46,086
Total loans held for investment | Current and accruing | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	19,774	16,230
Total loans held for investment | Current and accruing | C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	10,732	9,895
Total loans held for investment | Current and accruing | CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	7,730	7,530
Total loans held for investment | Current and accruing | REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,671	1,697
Total loans held for investment | Current and accruing | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	10,277	9,396
Total loans held for investment | Current and accruing | Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	$ 1,226	$ 1,338