SEGMENT INFORMATION, Classified by Major Geographic Areas (Details) £ in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2022 GBP (£)	Jan. 21, 2022 USD ($)	Jan. 21, 2022 GBP (£)	Sep. 30, 2021 USD ($)
Revenues:
Total net revenues	$ 2,673	$ 2,372	$ 5,454	$ 4,594
Pre-tax income
Total pre-tax income	433	447	991	846
Total assets:
Total assets	73,101		73,101					$ 61,891
Goodwill:
Goodwill	818		818					660
Charles Stanley
Goodwill:
Goodwill	159		159		£ 121	$ 164	£ 121
U.S.
Revenues:
Total net revenues	2,430	2,194	5,019	4,273
Pre-tax income
Total pre-tax income	406	415	937	812
Total assets:
Total assets	65,777		65,777					57,952
Goodwill:
Goodwill	619		619					619
Canada
Revenues:
Total net revenues	129	130	266	235
Pre-tax income
Total pre-tax income	14	25	32	26
Total assets:
Total assets	4,059		4,059					3,724
Goodwill:
Goodwill	25		25					25
Europe
Revenues:
Total net revenues	114	48	169	86
Pre-tax income
Total pre-tax income	13	$ 7	22	$ 8
Total assets:
Total assets	3,265		3,265					215
Goodwill:
Goodwill	$ 174		$ 174					$ 16