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FINANCIAL RISK MANAGEMENT ACTIVITIES - Fair Value of Financial Instruments (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Financial assets      
Carrying amount $ 188 $ 86 $ 147
Borrowings      
Financial liabilities      
Carrying amount 1,931 2,033 2,050
Fair value 2,131 2,135 2,084
Other investments      
Financial assets      
Carrying amount 188 170 147
Fair value 188 170 $ 147
Other investment, transferred as held for sale      
Financial assets      
Carrying amount $ 0 $ 84