BANK LOANS, NET, Held for Investment Loans and Held for Sale Loans (Details) $ in Millions	Sep. 30, 2025 USD ($) portfolio_segment	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)
Receivables [Abstract]
Number of loan portfolio segments | portfolio_segment	6
Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	$ 52,019	$ 46,451
Allowance for loan losses	(452)	(457)
Loans, net	$ 51,567	$ 45,994
ACL as a % of total loans held for investment	0.88%	0.99%
Accrued interest receivable on bank loans (included in “Other receivables, net”)	$ 216	$ 214
Accrued interest receivable on bank loans, location	Other Receivables	Other Receivables
Total loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	$ 51,603	$ 46,267
Allowance for loan losses	(452)	(457)	$ (474)	$ (396)
Total loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	51,603	46,267
Held for sale loans | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	416	184
SBL
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	19,775	16,233
SBL | Total loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	19,775	16,233
Allowance for loan losses	(8)	(6)	(7)	(3)
SBL | Total loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	19,775	16,233
C&I loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	10,777	9,953
C&I loans | Total loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	10,777	9,953
Allowance for loan losses	(148)	(173)	(214)	(226)
C&I loans | Total loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	10,777	9,953
CRE loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	7,840	7,615
CRE loans | Total loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	7,840	7,615
Allowance for loan losses	(182)	(188)	(161)	(87)
CRE loans | Total loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	7,840	7,615
REIT loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	1,690	1,716
REIT loans | Total loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	1,690	1,716
Allowance for loan losses	(52)	(23)	(16)	(21)
REIT loans | Total loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	1,690	1,716
Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	10,295	9,412
Residential mortgage loans | Total loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	10,295	9,412
Allowance for loan losses	(61)	(65)	(74)	(57)
Residential mortgage loans | Total loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	10,295	9,412
Tax-exempt loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	1,226	1,338
Tax-exempt loans | Total loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	1,226	1,338
Allowance for loan losses	(1)	(2)	$ (2)	$ (2)
Tax-exempt loans | Total loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	$ 1,226	$ 1,338