CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net income	$ 2,068	$ 1,739	$ 1,509
Adjustments to reconcile net income to net cash provided by/(used in) operating activities:
Depreciation and amortization	179	165	145
Deferred income taxes, net	(83)	(88)	(16)
Premium and discount amortization on available-for-sale securities and bank loans and net unrealized gain/loss on other investments	(36)	(49)	23
Provisions for credit losses and legal and regulatory proceedings	21	292	111
Share-based compensation expense	254	237	192
Unrealized (gain)/loss on company-owned life insurance policies, net of expenses	(233)	(96)	174
Other	22	10	49
Net change in:
Assets segregated for regulatory purposes excluding cash and cash equivalents	0	0	2,100
Collateralized agreements, net of collateralized financings	270	157	(37)
Loans (provided to) financial advisors, net of repayments	(223)	(7)	(120)
Brokerage client receivables and other receivables, net	(362)	257	(203)
Trading instruments, net	(34)	(33)	48
Derivative instruments, net	(151)	(130)	479
Other assets	9	(52)	(126)
Brokerage client payables and other payables	91	(6,088)	(4,213)
Accrued compensation, commissions and benefits	404	123	(76)
Purchases and originations of loans held for sale, net of proceeds from sales of securitizations and loans held for sale	(41)	49	33
Net cash provided by/(used in) operating activities	2,155	(3,514)	72
Cash flows from investing activities:
Increase in bank loans, net	(2,599)	(1,262)	(7,235)
Proceeds from sales of loans held for investment	415	680	213
Purchases of available-for-sale securities	(503)	(611)	(3,069)
Available-for-sale securities maturations, repayments and redemptions	2,010	1,262	1,712
Proceeds from sales of available-for-sale securities	0	0	52
Cash and cash equivalents acquired in business acquisitions, including those segregated for regulatory purposes, net of cash paid for acquisitions	0	0	1,461
Additions to property and equipment	(205)	(173)	(91)
(Purchases)/sales of Federal Reserve Bank (“FRB”) and Federal Home Loan Bank (“FHLB”) stock, net	0	(26)	0
Investment in note receivable	0	0	(125)
Renewable energy tax credit equity investments	(42)	(69)	0
(Purchases)/sales of other investments, net	20	(6)	24
Other investing activities, net	(64)	(69)	(93)
Net cash used in investing activities	(968)	(274)	(7,151)
Cash flows from financing activities:
Increase in bank deposits	1,811	2,842	6,269
Repurchases of common stock and share-based awards withheld for payment of withholding tax requirements	(984)	(862)	(216)
Dividends on common and preferred stock	(383)	(355)	(277)
Exercise of stock options and employee stock purchases	46	46	52
Redemption of preferred stock	0	(40)	0
Proceeds from FHLB advances	1,300	3,200	1,025
Repayments of FHLB advances and other borrowed funds	(1,350)	(3,391)	(967)
Other financing, net	(2)	(2)	(7)
Net cash provided by financing activities	438	1,438	5,879
Currency adjustment:
Effect of exchange rate changes on cash and cash equivalents, including those segregated for regulatory purposes	175	239	(590)
Net increase/(decrease) in cash and cash equivalents, including those segregated for regulatory purposes and restricted cash	1,800	(2,111)	(1,790)
Cash and cash equivalents, including those segregated for regulatory purposes and restricted cash at beginning of year	12,548	14,659	16,449
Cash and cash equivalents, including those segregated for regulatory purposes and restricted cash at end of year	14,348	12,548	14,659
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	10,998	9,313	6,178
Cash and cash equivalents segregated for regulatory purposes and restricted cash	3,350	3,235	8,481
Total cash and cash equivalents, including those segregated for regulatory purposes and restricted cash at end of year	14,348	12,548	14,659
Supplemental disclosures of cash flow information:
Cash paid for interest	2,119	1,310	323
Cash paid for income taxes, net	664	565	524
Cash outflows for lease liabilities	121	123	111
Non-cash right-of-use (“ROU”) lease assets recorded for new and modified leases	63	143	68
Restricted stock awards issued as consideration for TriState Capital acquisition	0	0	28
Effective settlement of note receivable for TriState Capital acquisition	0	0	123
Common stock
Supplemental disclosures of cash flow information:
Stock issued as consideration for TriState Capital acquisition	0	0	778
Preferred stock
Supplemental disclosures of cash flow information:
Stock issued as consideration for TriState Capital acquisition	$ 0	$ 0	$ 120