GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS, NET, Intangible Assets, by Type (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	$ 615	$ 634
Accumulated amortization, finite-lived intangible assets	(180)	(164)
Customer relationships
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	349	365
Accumulated amortization, finite-lived intangible assets	(127)	(127)
Core deposit intangible
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	89	89
Accumulated amortization, finite-lived intangible assets	(21)	(12)
Trade names
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	59	59
Accumulated amortization, finite-lived intangible assets	(13)	(10)
Developed technology
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	58	58
Accumulated amortization, finite-lived intangible assets	(17)	(10)
All other
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	3	6
Accumulated amortization, finite-lived intangible assets	(2)	(5)
Customer relationships
Intangible Assets [Line Items]
Gross carrying value, indefinite-lived assets	57	57
Accumulated amortization, indefinite-lived assets	$ 0	$ 0