SEGMENT INFORMATION, Information Concerning Operations (Details) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Mar. 31, 2024 USD ($) segment	Mar. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment			5
Net revenues:
Total net revenues	$ 3,118	$ 2,873	$ 6,131	$ 5,659
Pre-tax income/(loss):
Total pre-tax income	609	557	1,239	1,209
Net interest income (expense):
Net interest income	529	631	1,075	1,217
Total assets:
Total assets	81,232		81,232		$ 78,360
Goodwill and Intangible Assets:
Goodwill	1,442		1,442		1,437
Operating segments | Private Client Group
Net revenues:
Total net revenues	2,341	2,144	4,567	4,207
Pre-tax income/(loss):
Total pre-tax income	444	441	883	875
Net interest income (expense):
Net interest income	92	88	184	175
Total assets:
Total assets	13,194		13,194		12,375
Goodwill and Intangible Assets:
Goodwill	569		569		564
Operating segments | Capital Markets
Net revenues:
Total net revenues	321	302	659	597
Pre-tax income/(loss):
Total pre-tax income	(17)	(34)	(14)	(50)
Net interest income (expense):
Net interest income	2	1	3	1
Total assets:
Total assets	3,601		3,601		3,087
Goodwill and Intangible Assets:
Goodwill	275		275		275
Operating segments | Asset Management
Net revenues:
Total net revenues	252	216	487	423
Pre-tax income/(loss):
Total pre-tax income	100	82	193	162
Net interest income (expense):
Net interest income	3	3	6	5
Total assets:
Total assets	555		555		567
Goodwill and Intangible Assets:
Goodwill	69		69		69
Operating segments | Bank
Net revenues:
Total net revenues	424	540	865	1,048
Pre-tax income/(loss):
Total pre-tax income	75	91	167	227
Net interest income (expense):
Net interest income	413	530	839	1,021
Total assets:
Total assets	61,038		61,038		60,041
Goodwill and Intangible Assets:
Goodwill	529		529		529
Operating segments | Other
Net revenues:
Total net revenues	17	10	43	19
Pre-tax income/(loss):
Total pre-tax income	7	(23)	10	(5)
Net interest income (expense):
Net interest income	19	9	43	15
Total assets:
Total assets	2,844		2,844		$ 2,290
Intersegment eliminations
Net revenues:
Total net revenues	$ (237)	$ (339)	$ (490)	$ (635)