FAIR VALUE, Level 3 Financial Assets and Liabilities, Roll Forward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Sep. 30, 2022
Percentage of instruments measured at fair value on a recurring basis
Instruments measured at fair value, percentage of assets (in hundredths)	14.00%		14.00%		14.00%
Instruments measured at fair value, percentage of liabilities (in hundredths)	2.00%		2.00%		2.00%
Instruments measured at fair value, level 3, percentage of assets (in hundredths)	1.00%		1.00%		1.00%
Trading liabilities | Other
Changes in Level 3 recurring fair value measurements, liabilities [Roll Forward]
Fair value beginning of period		$ 0		$ 0
Total gains/(losses) included in earnings		(1)		(1)
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		(1)		(1)
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period		(1)		(1)
Derivative liabilities | Other
Changes in Level 3 recurring fair value measurements, liabilities [Roll Forward]
Fair value beginning of period	$ (4)		$ (3)	(1)
Total gains/(losses) included in earnings	0		(1)	1
Purchases and contributions	0		0	0
Sales and distributions	0		0	0
Transfers:
Into Level 3	0		0	0
Out of Level 3	0		0	0
Fair value end of period	(4)	0	(4)	0
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period	0		(1)	0
Trading assets | Trading assets
Changes in Level 3 recurring fair value measurements, assets [Roll Forward]
Fair value beginning of period	6	2	1	14
Total gains/(losses) included in earnings	0	0	0	2
Purchases and contributions	11	29	36	54
Sales and distributions	(14)	(18)	(34)	(57)
Transfers:
Into Level 3	0	0	0	0
Out of Level 3	0	0	0	0
Fair value end of period	3	13	3	13
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period	0	(1)	0	(1)
Derivative assets | Other
Changes in Level 3 recurring fair value measurements, assets [Roll Forward]
Fair value beginning of period		1
Total gains/(losses) included in earnings		(1)
Purchases and contributions		0
Sales and distributions		0
Transfers:
Into Level 3		0
Out of Level 3		0
Fair value end of period		0		0
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period		(1)
Other investments | All other
Changes in Level 3 recurring fair value measurements, assets [Roll Forward]
Fair value beginning of period	30	98	29	98
Total gains/(losses) included in earnings	(2)	0	(1)	0
Purchases and contributions	0	7	0	7
Sales and distributions	0	(40)	0	(40)
Transfers:
Into Level 3	0	0	0	0
Out of Level 3	0	(12)	0	(12)
Fair value end of period	28	53	28	53
Unrealized gains/(losses) for the period included in earnings for instruments held at the end of the reporting period	$ (2)	$ 0	$ (1)	$ 0