OTHER BORROWINGS, Schedule of Other Borrowings (Details) - USD ($) $ in Millions	Jun. 30, 2024	Sep. 30, 2023
Other Borrowings [Abstract]
Total FHLB advances	$ 950	$ 1,000
Total other borrowings	$ 1,049	$ 1,100
FHLB Advance Maturing March 2025 - December 2025
Other Borrowings [Abstract]
Weighted average interest rate (as a percent)	5.64%
Total FHLB advances	$ 650
FHLB Advance Maturing September 2024 - December 2028
Other Borrowings [Abstract]
Weighted average interest rate (as a percent)	4.62%
Total FHLB advances	$ 300
FHLB Advance Maturing December 2023 - March 2025
Other Borrowings [Abstract]
Weighted average interest rate (as a percent)		5.62%
Total FHLB advances		$ 850
FHLB Advance Maturing December 2023
Other Borrowings [Abstract]
Weighted average interest rate (as a percent)		5.70%
Total FHLB advances		$ 150
Subordinated notes due 2030
Other Borrowings [Abstract]
Subordinated notes - fixed-to-floating	99	100
Subordinated Debt
Other Borrowings [Abstract]
Unaccreted premium	$ 1	$ 2
Subordinated Debt | Subordinated notes due 2030
Other Borrowings [Abstract]
Weighted average interest rate (as a percent)	5.75%	5.75%