AVAILABLE-FOR-SALE SECURITIES, Narrative (Details) $ in Millions	9 Months Ended
	Jun. 30, 2023 USD ($) investmentPosition	Sep. 30, 2022 USD ($)
Debt Securities, Available-for-sale [Line Items]
Accrued interest excluded	$ 28	$ 24
Duration, available for sale securities	4 years 3 months 18 days
Fair value	$ 9,566	9,885
Federal National Mortgage Association (FNMA)
Debt Securities, Available-for-sale [Line Items]
Amortized cost basis	4,910
Fair value	4,310
Federal Home Loan Mortgage Corporation (FHLMC)
Debt Securities, Available-for-sale [Line Items]
Amortized cost basis	2,950
Fair value	2,570
Bank
Debt Securities, Available-for-sale [Line Items]
Amortized cost basis	10,672	11,100
Fair value	$ 9,566	$ 9,885
Bank | Agency mortgage-backed securities (“MBS”), collateralized mortgage obligations (“CMOs”) and asset-backed securities (“ABS”)
Debt Securities, Available-for-sale [Line Items]
Number of available-for-sale investment positions determined to be in an unrealized loss position | investmentPosition	1,079
Number of available-for-sale investment positions determined to be in an unrealized loss position continuously for less than 12 months | investmentPosition	144
Number of available-for-sale investment positions determined to be in an unrealized loss position continuously for 12 months or more | investmentPosition	935