FAIR VALUE, Carrying Amounts and Estimated Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Carrying amount
Financial assets:
Bank loans, net	$ 21,823	$ 21,125
Financial liabilities:
Bank deposits - certificates of deposit	912	1,017
Senior notes payable	2,045	2,045
Recurring | Total estimated fair value
Financial assets:
Bank loans, net	21,842	21,191
Financial liabilities:
Bank deposits - certificates of deposit	946	1,056
Senior notes payable	2,572	2,504
Recurring | Level 2 | Total estimated fair value
Financial assets:
Bank loans, net	105	72
Financial liabilities:
Bank deposits - certificates of deposit	0	0
Senior notes payable	2,572	2,504
Recurring | Level 3 | Total estimated fair value
Financial assets:
Bank loans, net	21,737	21,119
Financial liabilities:
Bank deposits - certificates of deposit	946	1,056
Senior notes payable	$ 0	$ 0