VARIABLE INTEREST ENTITIES, Primary Beneficiary - Carrying Value of Assets, Liabilities and Equity (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	$ 14,348	$ 12,548	$ 14,659	$ 16,449
Other assets	3,357	2,793
Total assets	82,992	78,360
Liabilities:
Other payables	1,938	1,931
Total liabilities	71,325	68,173
Noncontrolling interests	(6)	(27)
Variable Interest Entity, Primary Beneficiary
Assets:
Total assets	155	71
Liabilities:
Total liabilities	79	26
Variable Interest Entity, Primary Beneficiary | Carrying Amount
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	17	5
Other assets	119	46
Total assets	136	51
Liabilities:
Other payables	37	0
Total liabilities	37	0
Noncontrolling interests	$ (6)	$ (27)