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Financial Instruments - Fair Value of Long Term Debt (Details) - USD ($)
$ in Millions
Jun. 30, 2017
Dec. 31, 2016
Level 1    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value of long term debt $ 739 $ 725
Level 2    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value of long term debt 767 571
Level 3    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Fair value of long term debt $ 14 $ 15