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Financial Instruments and Risk Management (Credit Risk - Movement in the Allowance of Doubtful Accounts during the Year) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Notes to Consolidated Financial Statements [Abstract]    
Balance at start of period $ 11 $ 6
Additional allowance 1 5
Write offs (7) (1)
Reversals (1) 0
Change due to translation differences (1) 1
Balance at end of period $ 3 $ 11