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Significant Accounting Policies (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Jan. 01, 2018
Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Retained earnings (accumulated deficit) $ (20,228)     $ (20,210)
Deferred revenue 254     $ 205
Defined benefit plan, other cost (credit) 5 $ 2    
Adoption of new accounting guidance related to reclassification of certain tax effects $ 45 $ 0    
Accounting Standards Update 2016-16        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Retained earnings (accumulated deficit)     $ 406  
Decrease in deferred tax assets, net     (406)  
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Retained earnings (accumulated deficit)     $ 9