BANK LOANS, NET, Changes in the Allowance for Loan Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2022
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 396
Net (charge-offs)/recoveries:
Balance at end of period	408
Increase (decrease) in allowance for credit losses	12
Loans held for investment
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	396	$ 320
Total provision/(benefit) for credit losses	14	(11)
Net (charge-offs)/recoveries:
Charge-offs	(5)	(2)
Recoveries	3	1
Net (charge-offs)/recoveries	(2)	(1)
Foreign exchange translation adjustment	0	0
Balance at end of period	$ 408	$ 308
ACL by loan portfolio segment as a % of total ACL	100.00%	100.00%
Loans held for investment | SBL
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 3	$ 4
Total provision/(benefit) for credit losses	1	(1)
Net (charge-offs)/recoveries:
Charge-offs	0	0
Recoveries	0	0
Net (charge-offs)/recoveries	0	0
Foreign exchange translation adjustment	0	0
Balance at end of period	$ 4	$ 3
ACL by loan portfolio segment as a % of total ACL	1.00%	1.00%
Loans held for investment | C&I loans
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 226	$ 191
Total provision/(benefit) for credit losses	0	(10)
Net (charge-offs)/recoveries:
Charge-offs	(4)	(2)
Recoveries	0	0
Net (charge-offs)/recoveries	(4)	(2)
Foreign exchange translation adjustment	0	0
Balance at end of period	$ 222	$ 179
ACL by loan portfolio segment as a % of total ACL	54.40%	58.20%
Loans held for investment | CRE loans
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 87	$ 66
Total provision/(benefit) for credit losses	2	6
Net (charge-offs)/recoveries:
Charge-offs	(1)	0
Recoveries	3	0
Net (charge-offs)/recoveries	2	0
Foreign exchange translation adjustment	0	0
Balance at end of period	$ 91	$ 72
ACL by loan portfolio segment as a % of total ACL	22.30%	23.40%
Loans held for investment | REIT loans
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 21	$ 22
Total provision/(benefit) for credit losses	(6)	0
Net (charge-offs)/recoveries:
Charge-offs	0	0
Recoveries	0	0
Net (charge-offs)/recoveries	0	0
Foreign exchange translation adjustment	0	0
Balance at end of period	$ 15	$ 22
ACL by loan portfolio segment as a % of total ACL	3.70%	7.10%
Loans held for investment | Residential mortgage loans
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 57	$ 35
Total provision/(benefit) for credit losses	17	(6)
Net (charge-offs)/recoveries:
Charge-offs	0	0
Recoveries	0	1
Net (charge-offs)/recoveries	0	1
Foreign exchange translation adjustment	0	0
Balance at end of period	$ 74	$ 30
ACL by loan portfolio segment as a % of total ACL	18.10%	9.70%
Loans held for investment | Tax-exempt loans
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 2	$ 2
Total provision/(benefit) for credit losses	0	0
Net (charge-offs)/recoveries:
Charge-offs	0	0
Recoveries	0	0
Net (charge-offs)/recoveries	0	0
Foreign exchange translation adjustment	0	0
Balance at end of period	$ 2	$ 2
ACL by loan portfolio segment as a % of total ACL	0.50%	0.60%
Unfunded lending commitments
Net (charge-offs)/recoveries:
Unfunded lending commitments	$ 19		$ 19