GOODWILL AND IDENTIFIABLE INTANGIBLE ASSETS, NET, Intangible Assets, by Type (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	$ 612	$ 615
Accumulated amortization, finite-lived intangible assets	(216)	(180)
Customer relationships
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	347	349
Accumulated amortization, finite-lived intangible assets	(143)	(127)
Core deposit intangible
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	89	89
Accumulated amortization, finite-lived intangible assets	(30)	(21)
Trade names
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	59	59
Accumulated amortization, finite-lived intangible assets	(17)	(13)
Developed technology
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	58	58
Accumulated amortization, finite-lived intangible assets	(24)	(17)
All other
Intangible Assets [Line Items]
Gross carrying value, finite-lived intangible assets	2	3
Accumulated amortization, finite-lived intangible assets	(2)	(2)
Customer relationships
Intangible Assets [Line Items]
Gross carrying value, indefinite-lived assets	57	57
Accumulated amortization, indefinite-lived assets	$ 0	$ 0