AVAILABLE-FOR-SALE SECURITIES, Narrative (Details) $ in Millions	12 Months Ended
	Sep. 30, 2023 USD ($) investmentPosition	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)
Debt Securities, Available-for-sale [Line Items]
Accrued interest on available-for-sale securities, location	Other Receivables	Other Receivables
Fair value	$ 9,181	$ 9,885
Proceeds from sales of available-for-sale securities	0	52	$ 969
Bank
Debt Securities, Available-for-sale [Line Items]
Accrued interest on available-for-sale securities	$ 28	24
Average expected duration, available for sale securities	4 years 2 months 12 days
Amortized cost basis	$ 10,433	11,100
Fair value	$ 9,181	9,885
Bank | Agency MBS, CMOs, and ABS
Debt Securities, Available-for-sale [Line Items]
Number of available-for-sale investment positions determined to be in an unrealized loss position | investmentPosition	1,084
Number of available-for-sale investment positions determined to be in an unrealized loss position continuously for less than 12 months | investmentPosition	46
Number of available-for-sale investment positions determined to be in an unrealized loss position continuously for 12 months or more | investmentPosition	1,038
Proceeds from sales of available-for-sale securities	$ 0	$ 52	$ 969
Bank | Federal National Mortgage Association (FNMA)
Debt Securities, Available-for-sale [Line Items]
Amortized cost basis	4,760
Fair value	4,080
Bank | Federal Home Loan Mortgage Corporation (FHLMC)
Debt Securities, Available-for-sale [Line Items]
Amortized cost basis	2,850
Fair value	$ 2,420