LEASES (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Operating Lease, Cost	$ 121	$ 120
Finance Lease, Right-of-Use Asset, Amortization	15	13
Finance Lease, Interest Expense	7	6
Finance Lease, Cost	22	19
Short-term Lease, Cost	49	54
Variable Lease, Cost	71	64
Sublease Income	(2)	(1)
Lease, Cost	261	256
Operating Lease, Payments	127	126
Finance Lease, Interest Payment on Liability	7	6
Finance Lease, Principal Payments	11	$ 8
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	35		$ 185
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	57		178
Operating lease right-of-use assets	1,810		1,856
Property	56,009		56,325
Accumulated depreciation	(36,112)		(36,086)
Total Lease Assets	2,295		2,305
Operating lease liabilities - current	405		416
Finance Lease, Liability, Current	64		54
Operating lease liabilities - noncurrent	1,477		1,521
Finance Lease, Liability, Noncurrent	490		464
Total Lease Liabilities	$ 2,436		$ 2,455
Operating Lease, Weighted Average Remaining Lease Term	7 years 6 months		7 years 7 months 6 days
Finance Lease, Weighted Average Remaining Lease Term	11 years		11 years 7 months 6 days
Operating Lease, Weighted Average Discount Rate, Percent	3.72%		3.84%
Finance Lease, Weighted Average Discount Rate, Percent	5.15%		5.41%
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	$ 353
Finance Lease, Liability, Payments, Remainder of Fiscal Year	66
Lessee, Operating Lease, Liability, to be Paid, Year One	398
Finance Lease, Liability, to be Paid, Year One	84
Lessee, Operating Lease, Liability, Payments, Due Year Two	323
Finance Lease, Liability, Payments, Due Year Two	108
Lessee, Operating Lease, Liability, Payments, Due Year Three	253
Finance Lease, Liability, Payments, Due Year Three	54
Lessee, Operating Lease, Liability, Payments, Due Year Four	174
Finance Lease, Liability, to be Paid, Year Four	44
Lessee, Operating Lease, Liability, Payments, Due Year Five	704
Finance Lease, Liability, Payments, Due Year Five	383
Lessee, Operating Lease, Liability, Payments, Due	2,205
Finance Lease, Liability, Payment, Due	739
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	323
Finance Lease, Liability, Undiscounted Excess Amount	185
Operating Lease, Liability	1,882
Finance lease obligations 2	554
Lessee, Additional Leases Not yet Commenced, Assumptions and Judgment, Amount	$ 9
Lessee, Additional Leases Not yet Commenced, Term of Contract	10 years
Residual Value Guarantees [Member]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 805		$ 818
Guarantor Obligations, Current Carrying Value	19		22
Finance Leases [Member]
Property	712		665
Accumulated depreciation	$ (227)		$ (216)