VARIABLE INTEREST ENTITIES, Primary Beneficiary - Carrying Value of Assets, Liabilities and Equity (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	$ 12,548	$ 14,659	$ 16,449	$ 9,634
Other assets	2,793	2,452
Total assets	78,360	80,951
Liabilities:
Other payables	1,931	1,768
Total liabilities	68,173	71,519
Noncontrolling interests	(27)	(26)
Variable Interest Entity, Primary Beneficiary
Assets:
Total assets	71	76
Liabilities:
Total liabilities	26	23
Variable Interest Entity, Primary Beneficiary | Carrying Amount
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	5	5
Other assets	46	54
Total assets	51	59
Liabilities:
Other payables	0	0
Total liabilities	0	0
Noncontrolling interests	$ (27)	$ (26)