ACQUISITIONS, TriState Capital Narrative (Details) $ / shares in Units, shares in Thousands, $ in Millions		12 Months Ended
	Jun. 01, 2022 USD ($) day $ / shares shares	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 15, 2021 USD ($)
Business Acquisition [Line Items]
Restricted stock awards issued as consideration for TriState Capital acquisition		$ 0	$ 0	$ 28
TriState Capital
Business Acquisition [Line Items]
Note receivable					$ 125
Note receivable interest rate, year one					2.25%
Series A Non-Cumulative Perpetual Preferred Stock
Business Acquisition [Line Items]
Preferred stock percentage	6.75%
Series A Non-Cumulative Perpetual Preferred Stock | TriState Capital
Business Acquisition [Line Items]
Preferred stock percentage	6.75%
Series B Non-Cumulative Perpetual Preferred Stock
Business Acquisition [Line Items]
Preferred stock percentage	6.375%
Series B Non-Cumulative Perpetual Preferred Stock | TriState Capital
Business Acquisition [Line Items]
Preferred stock percentage	6.375%
TriState Capital
Business Acquisition [Line Items]
Restricted stock awards (in shares) | shares	551
Volume weighted average price, period | day	10
Restricted stock awards issued as consideration for TriState Capital acquisition	$ 28
Consideration transferred, note receivable	$ 123
TriState Capital | TriState Capital Common Stock
Business Acquisition [Line Items]
Share price (in dollars per share) | $ / shares	$ 6.00
Consideration transferred, share issuance ratio	0.25
TriState Capital | TriState Series C Convertible Preferred Stock
Business Acquisition [Line Items]
Share price (in dollars per share) | $ / shares	$ 30