FAIR VALUE, Carrying Amounts and Estimated Fair Value of Financial Instruments not Recorded on Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2024	Sep. 30, 2023
Carrying amount
Financial assets:
Bank loans, net	$ 45,021	$ 43,679
Financial liabilities:
Bank deposits - certificates of deposit	2,562	2,831
Carrying amount | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	99	100
Carrying amount | Senior notes payable
Financial liabilities:
Debt	2,039	2,039
Recurring | Total Estimated Fair Value
Financial assets:
Bank loans, net	43,991	42,764
Financial liabilities:
Bank deposits - certificates of deposit	2,557	2,817
Recurring | Total Estimated Fair Value | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	96	94
Recurring | Total Estimated Fair Value | Senior notes payable
Financial liabilities:
Debt	1,760	1,640
Recurring | Level 2 | Total Estimated Fair Value
Financial assets:
Bank loans, net	139	142
Financial liabilities:
Bank deposits - certificates of deposit	2,557	2,817
Recurring | Level 2 | Total Estimated Fair Value | Other borrowings - subordinated notes payable
Financial liabilities:
Debt	96	94
Recurring | Level 2 | Total Estimated Fair Value | Senior notes payable
Financial liabilities:
Debt	1,760	1,640
Recurring | Level 3 | Total Estimated Fair Value
Financial assets:
Bank loans, net	43,852	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