LOANS TO FINANCIAL ADVISORS, NET, Balance of Loans to Financial Advisors (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2023	Sep. 30, 2022
Receivables [Abstract]
Currently affiliated with the firm	$ 1,130	$ 1,173
No longer affiliated with the firm	8	8
Total loans to financial advisors	1,138	1,181
Allowance for credit losses	(30)	(29)
Loans to financial advisors, net	1,108	1,152
Accrued interest receivable on loans to financial advisors (included in “Other receivables, net”)	$ 5	$ 5
Allowance for credit losses as a percent of total loans to financial advisors	2.64%	2.46%
Past due period	180 days