SEGMENT INFORMATION, Classified by Major Geographic Areas (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Sep. 30, 2023
Net revenues:
Total revenues	$ 3,118	$ 2,873	$ 6,131	$ 5,659
Pre-tax income/(loss):
Total pre-tax income	609	557	1,239	1,209
Total assets:
Total assets	81,232		81,232		$ 78,360
Goodwill and Intangible Assets:
Goodwill	1,442		1,442		1,437
U.S.
Net revenues:
Total revenues	2,846	2,627	5,607	5,167
Pre-tax income/(loss):
Total pre-tax income	581	524	1,186	1,133
Total assets:
Total assets	75,338		75,338		72,506
Goodwill and Intangible Assets:
Goodwill	1,250		1,250		1,250
Canada
Net revenues:
Total revenues	155	144	294	278
Pre-tax income/(loss):
Total pre-tax income	37	36	64	67
Total assets:
Total assets	3,379		3,379		3,404
Goodwill and Intangible Assets:
Goodwill	25		25		25
Europe
Net revenues:
Total revenues	117	102	230	214
Pre-tax income/(loss):
Total pre-tax income	(9)	$ (3)	(11)	$ 9
Total assets:
Total assets	2,515		2,515		2,450
Goodwill and Intangible Assets:
Goodwill	$ 167		$ 167		$ 162