BANK LOANS, NET, Changes in the Allowance for Loan Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	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	$ 415		415
Increase (decrease) in allowance for credit losses	7		19
Loans held for investment
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	408	$ 308	396	$ 320
Total provision/(benefit) for credit losses	28	21	42	10
Net (charge-offs)/recoveries:
Charge-offs	(20)	(1)	(25)	(3)
Recoveries	0	0	3	1
Net (charge-offs)/recoveries	(20)	(1)	(22)	(2)
Foreign exchange translation adjustment	(1)	0	(1)	0
Balance at end of period	$ 415	$ 328	$ 415	$ 328
ACL by loan portfolio segment as a % of total ACL	100.00%	100.00%	100.00%	100.00%
Loans held for investment | SBL
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 4	$ 3	$ 3	$ 4
Total provision/(benefit) for credit losses	1	0	2	(1)
Net (charge-offs)/recoveries:
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Net (charge-offs)/recoveries	0	0	0	0
Foreign exchange translation adjustment	0	0	0	0
Balance at end of period	$ 5	$ 3	$ 5	$ 3
ACL by loan portfolio segment as a % of total ACL	1.20%	0.90%	1.20%	0.90%
Loans held for investment | C&I loans
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 222	$ 179	$ 226	$ 191
Total provision/(benefit) for credit losses	18	17	18	7
Net (charge-offs)/recoveries:
Charge-offs	(20)	(1)	(24)	(3)
Recoveries	0	0	0	0
Net (charge-offs)/recoveries	(20)	(1)	(24)	(3)
Foreign exchange translation adjustment	(1)	0	(1)	0
Balance at end of period	$ 219	$ 195	$ 219	$ 195
ACL by loan portfolio segment as a % of total ACL	52.80%	59.50%	52.80%	59.50%
Loans held for investment | CRE loans
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 91	$ 72	$ 87	$ 66
Total provision/(benefit) for credit losses	9	(1)	11	5
Net (charge-offs)/recoveries:
Charge-offs	0	0	(1)	0
Recoveries	0	0	3	0
Net (charge-offs)/recoveries	0	0	2	0
Foreign exchange translation adjustment	0	0	0	0
Balance at end of period	$ 100	$ 71	$ 100	$ 71
ACL by loan portfolio segment as a % of total ACL	24.10%	21.60%	24.10%	21.60%
Loans held for investment | REIT loans
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 15	$ 22	$ 21	$ 22
Total provision/(benefit) for credit losses	0	3	(6)	3
Net (charge-offs)/recoveries:
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Net (charge-offs)/recoveries	0	0	0	0
Foreign exchange translation adjustment	0	0	0	0
Balance at end of period	$ 15	$ 25	$ 15	$ 25
ACL by loan portfolio segment as a % of total ACL	3.60%	7.60%	3.60%	7.60%
Loans held for investment | Residential mortgage loans
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 74	$ 30	$ 57	$ 35
Total provision/(benefit) for credit losses	0	2	17	(4)
Net (charge-offs)/recoveries:
Charge-offs	0	0	0	0
Recoveries	0	0	0	1
Net (charge-offs)/recoveries	0	0	0	1
Foreign exchange translation adjustment	0	0	0	0
Balance at end of period	$ 74	$ 32	$ 74	$ 32
ACL by loan portfolio segment as a % of total ACL	17.80%	9.80%	17.80%	9.80%
Loans held for investment | Tax-exempt loans
Changes in the allowance for loan losses [Roll Forward]
Balance at beginning of period	$ 2	$ 2	$ 2	$ 2
Total provision/(benefit) for credit losses	0	0	0	0
Net (charge-offs)/recoveries:
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Net (charge-offs)/recoveries	0	0	0	0
Foreign exchange translation adjustment	0	0	0	0
Balance at end of period	$ 2	$ 2	$ 2	$ 2
ACL by loan portfolio segment as a % of total ACL	0.50%	0.60%	0.50%	0.60%
Unfunded lending commitments
Net (charge-offs)/recoveries:
Unfunded lending commitments	$ 21		$ 21		$ 19	$ 19