LEASE COMMITMENTS - LEASE ASSETS AND LIABILITIES (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets:
Operating lease assets	$ 1,062	$ 1,411
Finance lease assets	365	397
Total lease assets	1,427	1,808
Assets and Liabilities, Lessee [Abstract]
Current operating lease liabilities	473	579
Current finance lease liabilities	42	51
Non-current operating lease liabilities	641	872
Non-current finance lease liabilities	316	347
Total lease liabilities	$ 1,472	$ 1,849
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:DebtCurrent	us-gaap:DebtCurrent
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtNoncurrent	us-gaap:LongTermDebtNoncurrent