VARIABLE INTEREST ENTITIES, Primary Beneficiary - Carrying Value of Assets, Liabilities and Equity (Details) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018
Assets:
Cash, cash equivalents and cash segregated pursuant to regulations	$ 8,837	$ 5,971	$ 5,952	$ 5,941
Other assets	1,572	1,020
Total assets	44,682	38,830
Liabilities:
Other payables	1,243	518
Total liabilities	37,667	32,187
Noncontrolling interests	50	62
Total VIEs - primary beneficiary
Assets:
Cash, cash equivalents and cash segregated pursuant to regulations	7	7
Other investments	32	63
Other assets	240	75
Total assets	279	145
Liabilities:
Other payables	156	4
Total liabilities	156	4
Noncontrolling interests	$ 50	$ 60