GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS, NET, Intangible Assets, by Type (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	$ 634	$ 628
Accumulated amortization, finite-lived intangible assets	(164)	(119)
Customer relationships
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	365	361
Accumulated amortization, finite-lived intangible assets	(127)	(103)
Core deposit intangible
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	89	89
Accumulated amortization, finite-lived intangible assets	(12)	(3)
Trade names
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	59	57
Accumulated amortization, finite-lived intangible assets	(10)	(5)
Developed technology
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	58	58
Accumulated amortization, finite-lived intangible assets	(10)	(4)
All other
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	6	6
Accumulated amortization, finite-lived intangible assets	(5)	(4)
Customer relationships
Intangible Assets [Line Items]
Gross carrying value, indefinite-lived assets	57	57
Accumulated amortization, indefinite-lived assets	$ 0	$ 0