BANK LOANS, NET, Analysis of Payment Status of Loans Held for Investment (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023
Financing Receivable, Past Due [Line Items]
Performing nonaccrual loans	$ 89	$ 96
SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	16,233	14,606
C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	9,953	10,406
TDRs		21
CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	7,615	7,221
TDRs		3
REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,716	1,668
Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	9,412	8,662
Residential mortgage - first mortgage loans
Financing Receivable, Past Due [Line Items]
TDRs		10
Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,338	1,541
Total loans held for investment
Financing Receivable, Past Due [Line Items]
Total loans held for investment	46,267	44,104
Nonaccrual with allowance	144	104
Nonaccrual with no allowance	31	24
Total loans held for investment | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	16,233	14,606
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	9,953	10,406
Nonaccrual with allowance	58	69
Nonaccrual with no allowance	0	2
Total loans held for investment | CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	7,615	7,221
Nonaccrual with allowance	67	35
Nonaccrual with no allowance	18	13
Total loans held for investment | REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,716	1,668
Nonaccrual with allowance	19	0
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	9,412	8,662
Nonaccrual with allowance	0	0
Nonaccrual with no allowance	13	9
Total loans held for investment | Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,338	1,541
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	6	11
Total loans held for investment | Total past due and accruing | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	3	9
Total loans held for investment | Total past due and accruing | C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	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	3	2
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	6	11
Total loans held for investment | 30-89 days and accruing | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	3	9
Total loans held for investment | 30-89 days and accruing | C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	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	3	2
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	46,086	43,965
Total loans held for investment | Current and accruing | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	16,230	14,597
Total loans held for investment | Current and accruing | C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	9,895	10,335
Total loans held for investment | Current and accruing | CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	7,530	7,173
Total loans held for investment | Current and accruing | REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,697	1,668
Total loans held for investment | Current and accruing | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	9,396	8,651
Total loans held for investment | Current and accruing | Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	$ 1,338	$ 1,541