VARIABLE INTEREST ENTITIES, Primary Beneficiary - Carrying Value of Assets, Liabilities and Equity (Details) - USD ($) $ in Millions	Dec. 31, 2025	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	$ 13,570	$ 14,787	$ 13,580	$ 14,348
Other receivables	1,487	1,814
Other assets	3,682	3,515
Total assets	88,760	88,230
Liabilities:
Other payables	1,838	1,961
Total liabilities	76,186	75,726
Noncontrolling interests	4	1
Variable Interest Entity, Primary Beneficiary
Assets:
Total assets	117	93
Liabilities:
Total liabilities	54	39
Variable Interest Entity, Primary Beneficiary | Carrying amount
Assets:
Cash and cash equivalents and assets segregated for regulatory purposes and restricted cash	24	19
Other receivables	2	0
Other assets	59	55
Total assets	85	74
Liabilities:
Other payables	16	13
Total liabilities	16	13
Noncontrolling interests	$ 4	$ 1