SEGMENT INFORMATION, Classified by Major Geographic Areas (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Net revenues:
Total revenues	$ 7,990	$ 7,740	$ 7,274
Pre-tax income/(loss):
Total pre-tax income	1,052	1,375	1,311
Total assets:
Aggregate assets	47,482	38,830
Goodwill and Intangible Assets:
Goodwill	466	464	478
Capital Markets
Goodwill and Intangible Assets:
Goodwill	120	120	133
U.S.
Net revenues:
Total revenues	7,446	7,211	6,754
Pre-tax income/(loss):
Total pre-tax income	1,028	1,356	1,269
Total assets:
Aggregate assets	44,090	35,978
Goodwill and Intangible Assets:
Goodwill	433	433
Canada
Net revenues:
Total revenues	386	391	381
Pre-tax income/(loss):
Total pre-tax income	29	29	47
Total assets:
Aggregate assets	3,260	2,754
Goodwill and Intangible Assets:
Goodwill	24	23
Europe
Net revenues:
Total revenues	158	138	139
Pre-tax income/(loss):
Total pre-tax income	(5)	(10)	$ (5)
Total assets:
Aggregate assets	132	98
Goodwill and Intangible Assets:
Goodwill	9	8
Europe | Capital Markets
Pre-tax income/(loss):
Loss on sale of operations		$ 15
FRANCE | Capital Markets
Pre-tax income/(loss):
Loss on sale of operations	$ 7