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Summary of Significant Accounting Policies (Details 1) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Summary of Significant Accounting Policies (Amounts in paragraphs)      
Research and development expenses $ 639 $ 705 $ 712
Cash surrender value of life insurance $ 340 $ 304  
Percentage threshold net actuarial gains losses subject to amortization 10.00%    
Average future service period of employees 8 years    
Average remaining life expectancy of plan participants 20 years    
Stock plans, vesting period 3 years