FAIR VALUE, Significant Assumptions Used in Valuation of Level 3 Financial Instruments (Details) - Recurring $ in Millions	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value on a recurring basis	$ 12,366	$ 8,935
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Assets at fair value on a recurring basis	77	71
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	$ 52	$ 37
Discount rate | Private equity investments | Level 3 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Multiple applied to revenue	25	25
EBITDA Multiple | Private equity investments | Level 3 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Abstract]
Multiple applied to revenue	9.0	9.0