LEASES - Operating Lease Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Leases [Abstract]
Operating lease assets	$ 350	$ 321
Operating lease liabilities	$ 372	$ 345
Weighted-average remaining lease term (years)	5 years 6 months
Weighted-average discount rate	3.80%
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssets
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrentAndNoncurrent