DERIVATIVE ASSETS AND DERIVATIVE LIABILITIES, Derivative Gain (Loss) Recognized in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate (cash flow hedges)	$ (34)	$ (61)	$ 33
Total gains/(losses) in AOCI, net of taxes	(29)	(39)	61
Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate (cash flow hedges)	(34)	(61)	33
Foreign exchange
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange (net investment hedges)	$ 5	$ 22	$ 28