FAIR VALUE, Level 3 Financial Assets and Liabilities, Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Percentage of instruments measured at fair value on a recurring basis
Instruments measured at fair value, percentage of assets (in hundredths)	23.00%		19.00%
Instruments measured at fair value, percentage of liabilities (in hundredths)	1.00%		2.00%
Instruments measured at fair value, level 3, percentage of assets (in hundredths)	1.00%		1.00%
Trading liabilities | Other
Changes in Level 3 recurring fair value measurements, liabilities [Roll Forward]
Fair value beginning of period		$ (1)
Total gains/(losses) included in earnings		0
Purchases and contributions		1
Sales and distributions		(1)
Transfers:
Into Level 3		0
Out of Level 3		0
Fair value end of period		(1)
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period		0
Derivative liabilities | Other
Changes in Level 3 recurring fair value measurements, liabilities [Roll Forward]
Fair value beginning of period	$ (5)
Total gains/(losses) included in earnings	4
Purchases and contributions	0
Sales and distributions	0
Transfers:
Into Level 3	0
Out of Level 3	0
Fair value end of period	(1)
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period	3
Trading assets | Trading assets
Changes in Level 3 recurring fair value measurements, assets [Roll Forward]
Fair value beginning of period	12	3
Total gains/(losses) included in earnings	2	(1)
Purchases and contributions	6	31
Sales and distributions	(17)	(14)
Transfers:
Into Level 3	0	0
Out of Level 3	0	0
Fair value end of period	3	19
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period	3	0
Private equity and other investments | Private equity investments
Changes in Level 3 recurring fair value measurements, assets [Roll Forward]
Fair value beginning of period	37	63
Total gains/(losses) included in earnings	15	0
Purchases and contributions	0	0
Sales and distributions	0	(1)
Transfers:
Into Level 3	0	0
Out of Level 3	0	0
Fair value end of period	52	62
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period	15	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	24
Total gains/(losses) included in earnings	0	0
Purchases and contributions	0	0
Sales and distributions	0	0
Transfers:
Into Level 3	0	0
Out of Level 3	0	0
Fair value end of period	22	24
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period	$ 0	$ 0