VARIABLE INTEREST ENTITIES, Primary Beneficiary - Carrying Value of Assets, Liabilities and Equity (Details) - USD ($) $ in Millions	Jun. 30, 2024	Sep. 30, 2023	Jun. 30, 2023	Sep. 30, 2022
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	$ 12,736	$ 12,548	$ 12,214	$ 14,659
Other assets	3,222	2,793
Total assets	80,628	78,360
Liabilities:
Other payables	2,084	1,931
Total liabilities	69,438	68,173
Noncontrolling interests	(7)	(27)
Variable Interest Entity, Primary Beneficiary
Assets:
Total assets	166	71
Liabilities:
Total liabilities	93	26
Variable Interest Entity, Primary Beneficiary | Carrying amount
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	15	5
Other assets	124	46
Total assets	139	51
Liabilities:
Other payables	42	0
Total liabilities	42	0
Noncontrolling interests	$ (7)	$ (27)