FAIR VALUE, Carrying Amounts and Estimated Fair Value of Financial Instruments not Recorded on Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2024	Sep. 30, 2023
Subordinated Debt | Subordinated Notes Due 2030
Financial liabilities:
Interest rate	5.75%
Carrying Amount
Financial assets:
Bank loans, net	$ 45,879	$ 43,679
Financial liabilities:
Bank deposits - certificates of deposit	2,612	2,831
Carrying Amount | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	99	100
Carrying Amount | Senior notes payable
Financial liabilities:
Debt	2,040	2,039
Recurring | Total Estimated Fair Value
Financial assets:
Bank loans, net	45,185	42,764
Financial liabilities:
Bank deposits - certificates of deposit	2,623	2,817
Recurring | Total Estimated Fair Value | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	97	94
Recurring | Total Estimated Fair Value | Senior notes payable
Financial liabilities:
Debt	1,874	1,640
Recurring | Level 2 | Total Estimated Fair Value
Financial assets:
Bank loans, net	183	142
Financial liabilities:
Bank deposits - certificates of deposit	2,623	2,817
Recurring | Level 2 | Total Estimated Fair Value | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	97	94
Recurring | Level 2 | Total Estimated Fair Value | Senior notes payable
Financial liabilities:
Debt	1,874	1,640
Recurring | Level 3 | Total Estimated Fair Value
Financial assets:
Bank loans, net	45,002	42,622
Financial liabilities:
Bank deposits - certificates of deposit	0	0
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