FAIR VALUE, Level 3 Financial Assets and Liabilities, Roll Forward (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Trading instruments | Other liabilities
Changes in Level 3 curring fair value measurements, liabilities [Roll Forward]
Fair value beginning of year	$ (1)	$ (7)
Total gains/(losses) included in earnings	0	2
Purchases and contributions	2	19
Sales and distributions	(1)	(15)
Transfers:
Into Level 3	0	0
Out of Level 3	0	0
Fair value end of year	0	(1)
Unrealized gains/(losses) for the year included in earnings for instruments held at the end of the year	0	0
Derivative liabilities | Other liabilities
Changes in Level 3 curring fair value measurements, liabilities [Roll Forward]
Fair value beginning of year	0
Total gains/(losses) included in earnings	(5)
Purchases and contributions	0
Sales and distributions	0
Transfers:
Into Level 3	0
Out of Level 3	0
Fair value end of year	(5)	0
Unrealized gains/(losses) for the year included in earnings for instruments held at the end of the year	(5)
Trading instruments | Other
Changes in Level 3 recurring fair value measurements, assets [Roll Forward]
Fair value beginning of year	3	1
Total gains/(losses) included in earnings	(4)	(3)
Purchases and contributions	70	109
Sales and distributions	(57)	(104)
Transfers:
Into Level 3	0	0
Out of Level 3	0	0
Fair value end of year	12	3
Unrealized gains/(losses) for the year included in earnings for instruments held at the end of the year	(1)	0
Other investments | Other investments - private equity
Changes in Level 3 recurring fair value measurements, assets [Roll Forward]
Fair value beginning of year	63	56
Total gains/(losses) included in earnings	(29)	4
Purchases and contributions	4	3
Sales and distributions	(1)	0
Transfers:
Into Level 3	0	0
Out of Level 3	0	0
Fair value end of year	37	63
Unrealized gains/(losses) for the year included in earnings for instruments held at the end of the year	(29)	4
Other investments | Other investments - private equity | Other Expense
Transfers:
Unrealized gains/(losses) for the year included in earnings for instruments held at the end of the year	(20)
Other investments | All other
Changes in Level 3 recurring fair value measurements, assets [Roll Forward]
Fair value beginning of year	24	67
Total gains/(losses) included in earnings	(2)	(3)
Purchases and contributions	0	0
Sales and distributions	0	(40)
Transfers:
Into Level 3	0	0
Out of Level 3	0	0
Fair value end of year	22	24
Unrealized gains/(losses) for the year included in earnings for instruments held at the end of the year	$ (2)	$ (1)