BANK LOANS, NET, Held for Sale and Held for Investment (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable on bank loans, location	Other receivables, net		Other receivables, net
Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	$ 44,570		$ 44,249
Allowance for credit losses	(471)		(474)
Loans, net	$ 44,099		$ 43,775
ACL as a % of total loans held for investment	1.06%		1.07%
Accrued interest receivable on bank loans (included in “Other receivables, net”)	$ 212		$ 200
Net unamortized discounts, unearned income, and deferred loan fees and costs	28		52
Loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	44,424		44,104
Allowance for credit losses	(471)	$ (479)	(474)	$ (415)	$ (408)	$ (396)
Loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	44,424		44,104
Loans held for sale | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	146		145
SBL
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	14,610		14,606
SBL | Loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	14,610		14,606
Allowance for credit losses	(6)	(7)	(7)	(5)	(4)	(3)
SBL | Loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	14,610		14,606
C&I loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	10,190		10,406
C&I loans | Loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	10,190		10,406
Allowance for credit losses	(196)	(211)	(214)	(219)	(222)	(226)
C&I loans | Loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	10,190		10,406
CRE loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	7,462		7,221
CRE loans | Loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	7,462		7,221
Allowance for credit losses	(181)	(174)	(161)	(100)	(91)	(87)
CRE loans | Loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	7,462		7,221
REIT loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	1,701		1,668
REIT loans | Loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	1,701		1,668
Allowance for credit losses	(19)	(17)	(16)	(15)	(15)	(21)
REIT loans | Loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	1,701		1,668
Residential mortgage loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	9,016		8,662
Residential mortgage loans | Loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	9,016		8,662
Allowance for credit losses	(67)	(68)	(74)	(74)	(74)	(57)
Residential mortgage loans | Loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	9,016		8,662
Tax-exempt loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	1,445		1,541
Tax-exempt loans | Loans held for investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	1,445		1,541
Allowance for credit losses	(2)	$ (2)	(2)	$ (2)	$ (2)	$ (2)
Tax-exempt loans | Loans held for investment | Nonrelated party
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans held for investment	$ 1,445		$ 1,541