DERIVATIVE ASSETS AND DERIVATIVE LIABILITIES, Derivative Gain (Loss) Recognized in AOCI (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedges	$ (43)	$ (13)	$ (33)	$ (30)
Total gains/(losses) in AOCI, net of taxes	9	(24)	6	(4)
Interest rate
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedges	(43)	(13)	(33)	(30)
Foreign exchange
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange (net investment hedges)	$ 52	$ (11)	$ 39	$ 26