FAIR VALUE, Carrying Amounts and Estimated Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022
Carrying amount
Financial assets:
Bank loans, net	$ 43,503	$ 43,167
Financial liabilities:
Bank deposits - certificates of deposit	2,656	999
Carrying amount | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	100	100
Carrying amount | Senior notes payable
Financial liabilities:
Debt	2,038	2,038
Recurring | Total estimated fair value
Financial assets:
Bank loans, net	42,952	42,470
Financial liabilities:
Bank deposits - certificates of deposit	2,643	979
Recurring | Total estimated fair value | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	92	95
Recurring | Total estimated fair value | Senior notes payable
Financial liabilities:
Debt	1,779	1,706
Recurring | Level 2 | Total estimated fair value
Financial assets:
Bank loans, net	26	134
Financial liabilities:
Bank deposits - certificates of deposit	2,643	400
Recurring | Level 2 | Total estimated fair value | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	92	95
Recurring | Level 2 | Total estimated fair value | Senior notes payable
Financial liabilities:
Debt	1,779	1,706
Recurring | Level 3 | Total estimated fair value
Financial assets:
Bank loans, net	42,926	42,336
Financial liabilities:
Bank deposits - certificates of deposit	0	579
Recurring | Level 3 | Total estimated fair value | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	0	0
Recurring | Level 3 | Total estimated fair value | Senior notes payable
Financial liabilities:
Debt	$ 0	$ 0