LOANS TO FINANCIAL ADVISORS, NET, Balance of Loans to Financial Advisors (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2022	Sep. 30, 2021
Receivables [Abstract]
Currently affiliated with the firm	$ 1,144	$ 1,074
No longer affiliated with the firm	9	10
Total loans to financial advisors	1,153	1,084
Allowance for credit losses	(29)	(27)
Loans to financial advisors, net	1,124	1,057
Accrued interest receivable on loans to financial advisors	$ 5	$ 4
Allowance for credit losses as a percent of the loan portfolio	2.52%	2.49%
Past due period	180 days