FAIR VALUE, Carrying Amounts and Estimated Fair Value of Financial Instruments not Recorded on Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Subordinated Debt | Subordinated Notes Due 2030
Financial liabilities:
Interest rate	5.75%
Carrying Amount
Financial assets:
Bank loans, net	$ 43,679	$ 43,167
Financial liabilities:
Bank deposits - certificates of deposit	2,831	999
Carrying Amount | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	100	100
Carrying Amount | Senior notes payable
Financial liabilities:
Debt	2,039	2,038
Recurring | Total Estimated Fair Value
Financial assets:
Bank loans, net	42,764	42,470
Financial liabilities:
Bank deposits - certificates of deposit	2,817	979
Recurring | Total Estimated Fair Value | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	94	95
Recurring | Total Estimated Fair Value | Senior notes payable
Financial liabilities:
Debt	1,640	1,706
Recurring | Level 2 | Total Estimated Fair Value
Financial assets:
Bank loans, net	142	134
Financial liabilities:
Bank deposits - certificates of deposit	2,817	400
Recurring | Level 2 | Total Estimated Fair Value | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	94	95
Recurring | Level 2 | Total Estimated Fair Value | Senior notes payable
Financial liabilities:
Debt	1,640	1,706
Recurring | Level 3 | Total Estimated Fair Value
Financial assets:
Bank loans, net	42,622	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