VARIABLE INTEREST ENTITIES, Primary Beneficiary - Carrying Value of Assets, Liabilities and Equity (Details) - USD ($) $ in Millions	Dec. 31, 2021	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	$ 14,107	$ 16,449	$ 11,396	$ 9,634
Other assets	2,388	2,257
Total assets	68,461	61,891
Liabilities:
Other payables	1,524	1,701
Total liabilities	59,809	53,588
Noncontrolling interests	52	58
Variable Interest Entity, Primary Beneficiary
Assets:
Total assets	191	192
Liabilities:
Total liabilities	80	71
Variable Interest Entity, Primary Beneficiary | Carrying amount
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	7	10
Other investments	47	63
Other assets	114	105
Total assets	168	178
Liabilities:
Other payables	44	45
Total liabilities	44	45
Noncontrolling interests	$ 51	$ 58