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Financial Instruments and Risk Management (Credit Risk - Maximum Exposure to Credit Risk) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Maximum Exposure to credit risk Financial assets [Line Items]    
Carrying amount $ 1,475 $ 1,406
Cash and cash equivalents [Member]    
Maximum Exposure to credit risk Financial assets [Line Items]    
Carrying amount 83 87
Short term investments and deposits [Member]    
Maximum Exposure to credit risk Financial assets [Line Items]    
Carrying amount 90 29
Trade receivables [Member]    
Maximum Exposure to credit risk Financial assets [Line Items]    
Carrying amount 932 966
Other receivables [Member]    
Maximum Exposure to credit risk Financial assets [Line Items]    
Carrying amount 86 59
Financial assets available for sale [Member]    
Maximum Exposure to credit risk Financial assets [Line Items]    
Carrying amount 212 253
Other non-current assets [Member]    
Maximum Exposure to credit risk Financial assets [Line Items]    
Carrying amount $ 72 $ 12