GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS, NET, Net Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Finite-lived Intangible Assets [Roll Forward]
Intangible assets (beginning of the period)	$ 147	$ 161
Additions		1
Amortization expense	(13)	(15)
Intangible assets (beginning of the period)	134	147
Private Client Group
Finite-lived Intangible Assets [Roll Forward]
Intangible assets (beginning of the period)	35	41
Additions		0
Amortization expense	(4)	(6)
Intangible assets (beginning of the period)	31	35
Capital Markets
Finite-lived Intangible Assets [Roll Forward]
Intangible assets (beginning of the period)	17	20
Additions		1
Amortization expense	(4)	(4)
Intangible assets (beginning of the period)	13	17
Asset Management
Finite-lived Intangible Assets [Roll Forward]
Intangible assets (beginning of the period)	95	100
Additions		0
Amortization expense	(5)	(5)
Intangible assets (beginning of the period)	$ 90	$ 95