VARIABLE INTEREST ENTITIES, Primary Beneficiary - Carrying Value of Assets, Liabilities and Equity (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018
Assets:
Cash, cash equivalents and cash segregated pursuant to regulations	$ 14,693	$ 5,971	$ 6,119	$ 5,941
Other assets	1,341	1,020
Total assets	49,809	38,830
Liabilities:
Other payables	1,034	518
Total liabilities	42,975	32,187
Noncontrolling interests	36	62
Total VIEs - primary beneficiary
Assets:
Cash, cash equivalents and cash segregated pursuant to regulations	6	7
Other investments	33	63
Other assets	70	75
Total assets	109	145
Liabilities:
Other payables	4	4
Total liabilities	4	4
Noncontrolling interests	$ 35	$ 60