FAIR VALUE, Level 3 Financial Assets and Liabilities, Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
Percentage of instruments measured at fair value on a recurring basis
Instruments measured at fair value, percentage of assets (in hundredths)	15.00%		15.00%		12.00%
Instruments measured at fair value, percentage of liabilities (in hundredths)	1.00%		1.00%		2.00%
Instruments measured at fair value, level 3, percentage of assets (in hundredths)	1.00%		1.00%		2.00%
Trading instruments | Other
Changes in Level 3 recurring fair value measurements, liabilities [Roll Forward]
Fair value beginning of period	$ 0	$ (7)	$ (1)	$ (7)
Total gains/(losses) included in earnings	0	0	0	2
Purchases and contributions	0	7	2	16
Sales and distributions	0	(3)	(1)	(14)
Transfers:
Into Level 3	0	0	0	0
Out of Level 3	0	0	0	0
Fair value end of period	0	(3)	0	(3)
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period	0	0	0	0
Trading instruments | Trading instruments
Changes in Level 3 recurring fair value measurements, assets [Roll Forward]
Fair value beginning of period	21	2	3	1
Total gains/(losses) included in earnings	(5)	(1)	(2)	(1)
Purchases and contributions	11	26	64	86
Sales and distributions	(12)	(26)	(50)	(85)
Transfers:
Into Level 3	0	0	0	0
Out of Level 3	0	0	0	0
Fair value end of period	15	1	15	1
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period	2	1	1	1
Private equity and other investments | Private equity investments
Changes in Level 3 recurring fair value measurements, assets [Roll Forward]
Fair value beginning of period	30	59	63	56
Total gains/(losses) included in earnings	0	0	(32)	0
Purchases and contributions	0	0	0	3
Sales and distributions	0	0	(1)	0
Transfers:
Into Level 3	0	0	0	0
Out of Level 3	0	0	0	0
Fair value end of period	30	59	30	59
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period	0	0	(32)	0
Private equity and other investments | All other
Changes in Level 3 recurring fair value measurements, assets [Roll Forward]
Fair value beginning of period	22	67	24	67
Total gains/(losses) included in earnings	0	(2)	(2)	(2)
Purchases and contributions	0	0	0	0
Sales and distributions	0	0	0	0
Transfers:
Into Level 3	0	0	0	0
Out of Level 3	0	0	0	0
Fair value end of period	22	65	22	65
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period	$ 0	$ (2)	$ (2)	$ (2)