FAIR VALUE, Level 3 Financial Assets and Liabilities, Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Percentage of instruments measured at fair value on a recurring basis [Abstract]
Instruments measured at fair value, percentage of assets (in hundredths)	19.00%	12.00%
Instruments measured at fair value, percentage of liabilities (in hundredths)	2.00%	2.00%
Instruments measured at fair value, Level 3, percentage of assets (in hundredths)	1.00%	2.00%
Other investments | Private Equity Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net unrealized gains/(losses) on our Level 3 private equity investments	$ (29)	$ 4
Other investments | Other Expense | Private Equity Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net unrealized gains/(losses) on our Level 3 private equity investments	$ (20)