VARIABLE INTEREST ENTITIES, Primary Beneficiary - Carrying Value of Assets, Liabilities and Equity (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Assets:
Cash and cash equivalents and assets segregated pursuant to regulations	$ 11,396	$ 9,634	$ 6,690	$ 5,971
Other receivables, net	850	927
Other assets	1,663	1,525
Total assets	53,657	47,482
Liabilities:
Other payables	1,710	1,513
Total liabilities	46,219	40,306
Noncontrolling interests	75	62
Variable Interest Entity, Primary Beneficiary
Assets:
Total assets	234	221
Liabilities:
Total liabilities	93	94
Variable Interest Entity, Primary Beneficiary | Carrying amount
Assets:
Cash and cash equivalents and assets segregated pursuant to regulations	8	9
Other investments	46	37
Other receivables, net	5	0
Other assets	158	164
Total assets	217	210
Liabilities:
Other payables	69	76
Total liabilities	69	76
Noncontrolling interests	$ 72	$ 62