FAIR VALUE, Significant Assumptions Used in Valuation of Level 3 Financial Instruments (Details) - Recurring $ in Millions	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value on a recurring basis	$ 5,473	$ 4,504
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value on a recurring basis	73	90
Private equity investments | Level 3 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value on a recurring basis	$ 30	$ 63
Discount rate | Private equity investments | Level 3 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Multiple applied to revenue	0.25	0.25
EBITDA Multiple | Private equity investments | Level 3 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Multiple applied to revenue	9.00	12.50