BANK LOANS, NET, Analysis of Payment Status of Loans Held for Investment and Collateral Dependent Loans (Details) - USD ($) $ in Millions	Sep. 30, 2022	Sep. 30, 2021
Financing Receivable, Past Due [Line Items]
Total loans held for investment	$ 43,635	$ 25,314
Performing nonaccrual loans	63	61
SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	15,297	6,106
C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	11,173	8,440
TDRs	11
Impaired loans with allowance for loan losses, gross recorded investment	11
CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	6,549	2,872
TDRs	9	12
Impaired loans with allowance for loan losses, gross recorded investment	21	20
REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,592	1,112
Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	7,386	5,318
Impaired loans with allowance for loan losses, gross recorded investment	6	5
Residential mortgage - first mortgage loans
Financing Receivable, Past Due [Line Items]
TDRs	10	13
Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,501	1,321
Total loans held for investment
Financing Receivable, Past Due [Line Items]
Total loans held for investment	43,498	25,169
Nonaccrual with allowance	44	41
Nonaccrual with no allowance	30	33
Total loans held for investment | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	15,297	6,106
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	11,173	8,440
Nonaccrual with allowance	32	39
Nonaccrual with no allowance	0	0
Total loans held for investment | CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	6,549	2,872
Nonaccrual with allowance	12	0
Nonaccrual with no allowance	16	20
Total loans held for investment | REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,592	1,112
Nonaccrual with allowance	0	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	7,386	5,318
Nonaccrual with allowance	0	2
Nonaccrual with no allowance	14	13
Total loans held for investment | Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,501	1,321
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	4	2
Total loans held for investment | Total past due and accruing | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
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	4	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	4	2
Total loans held for investment | 30-89 days and accruing | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	0	0
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	4	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	43,420	25,093
Total loans held for investment | Current and accruing | SBL
Financing Receivable, Past Due [Line Items]
Total loans held for investment	15,297	6,106
Total loans held for investment | Current and accruing | C&I loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	11,141	8,401
Total loans held for investment | Current and accruing | CRE loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	6,521	2,852
Total loans held for investment | Current and accruing | REIT loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,592	1,112
Total loans held for investment | Current and accruing | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	7,368	5,301
Total loans held for investment | Current and accruing | Tax-exempt loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	1,501	1,321
One-to-four family residential mortgage loans | Total past due and accruing | Residential mortgage loans
Financing Receivable, Past Due [Line Items]
Total loans held for investment	$ 5	$ 4