VARIABLE INTEREST ENTITIES, Primary Beneficiary - Carrying Value of Assets, Liabilities and Equity (Details) - USD ($) $ in Millions	Mar. 31, 2022	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	$ 14,852	$ 16,449	$ 10,275	$ 9,634
Other assets	2,333	2,257
Total assets	73,101	61,891
Liabilities:
Other payables	1,762	1,701
Other borrowings	856	858
Total liabilities	64,492	53,588
Noncontrolling interests	7	58
Variable Interest Entity, Primary Beneficiary
Assets:
Total assets	154	192
Liabilities:
Total liabilities	64	71
Variable Interest Entity, Primary Beneficiary | Carrying amount
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	6	10
Other investments	0	63
Other assets	125	105
Total assets	131	178
Liabilities:
Other payables	27	45
Other borrowings	2	0
Total liabilities	29	45
Noncontrolling interests	$ 5	$ 58