LEASES (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Operating Lease Cost	$ 5	$ 5
Short-term Lease Cost	6	6
Variable Lease, Cost	2	2
Lease, Cost	13	13
Operating cash flows for operating leases	5	$ 5
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	0		$ 48
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	0		3
Operating lease right-of-use assets	119		123
Finance Lease, Right-of-Use Asset	15		15
Accumulated depreciation	(5,865)		(5,824)
Total Lease Assets	125		130
Operating lease liabilities - current	19		19
Finance Lease, Liability, Current	2		2
Operating lease liabilities - noncurrent	101		105
Finance Lease, Liability, Noncurrent	4		5
Total Lease Liabilities	$ 126		$ 131
Operating Lease, Weighted Average Remaining Lease Term	7 years 3 months 18 days		7 years 6 months
Finance Lease, Weighted Average Remaining Lease Term	3 years 2 months 12 days		3 years 4 months 24 days
Operating Lease, Weighted Average Discount Rate, Percent	3.27%		3.28%
Finance Lease, Weighted Average Discount Rate, Percent	3.62%		3.62%
Lessee, Operating Lease, Liability, Payments, Remainder of 2020	$ 17
Finance Lease, Liability, Payments, Due 2020	2
Lessee, Operating Lease, Liability, Payments, Due 2021	22
Finance Lease, Liability, Payments, Due 2021	2
Lessee, Operating Lease, Liability, Payments, Due 2022	20
Finance Lease, Liability, Payments, Due 2022	2
Lessee, Operating Lease, Liability, Payments, Due 2023	20
Finance Lease, Liability, Payments, Due 2023	1
Lessee, Operating Lease, Liability, Payments, Due 2024	18
Finance Lease, Liability, Payments, Due 2024	0
Lessee, Operating Lease, Liability, Payments, Due 2025 and thereafter	38
Finance Lease, Liability, Payments, Due 2025 and thereafter	0
Lessee, Operating Lease, Liability, Payments, Due	135
Finance Lease, Liability, Payment, Due	7
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	15
Finance Lease, Liability, Undiscounted Excess Amount	1
Operating Lease, Liability	120
Finance Lease, Liability	6
finance leases [Member]
Accumulated depreciation	$ (9)		$ (8)

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