ACQUISITIONS, Narrative (Details) £ / shares in Units, $ / shares in Units, £ in Millions, $ in Millions				12 Months Ended
	Oct. 20, 2021 USD ($) $ / shares	Jul. 29, 2021 GBP (£)	Jul. 28, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jul. 29, 2021 USD ($)	Jul. 29, 2021 £ / shares	Sep. 30, 2020 USD ($)
Business Acquisition [Line Items]
Goodwill additions				$ 193
Assets segregated for regulatory purposes and restricted cash				11,348			$ 4,244
NWPS
Business Acquisition [Line Items]
Goodwill additions				139
Intangible assets acquired				$ 96
Intangible asset useful life				24 years 9 months 18 days
Financo
Business Acquisition [Line Items]
Goodwill additions				$ 30
Intangible assets acquired				$ 9
Intangible asset useful life				9 months
Goodwill tax deductible period				15 years
Cebile
Business Acquisition [Line Items]
Goodwill additions				$ 24
Intangible assets acquired				$ 4
Intangible asset useful life				2 years 6 months
Charles Stanley
Business Acquisition [Line Items]
Share price (in usd per share) | £ / shares						£ 5.15
Acquisition consideration		£ 279	$ 387
Consideration loan alternative, interest rate, year one					0.10%
Consideration loan alternative, interest rate, maximum					1.50%
Assets segregated for regulatory purposes and restricted cash					$ 400
TriState Capital | Subsequent Event
Business Acquisition [Line Items]
Acquisition consideration	$ 1,100
TriState Capital | Subsequent Event | TriState Capital Common Stock
Business Acquisition [Line Items]
Cash consideration per share (in dollars per share) | $ / shares	$ 6.00
Consideration transferred, share issuance ratio	0.25
Market value of per share consideration (in dollars per share) | $ / shares	$ 31.09
TriState Capital | Subsequent Event | TriState Series C Convertible Preferred Stock
Business Acquisition [Line Items]
Cash consideration per share (in dollars per share) | $ / shares	$ 30