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Cash Flow Information (Cash Payments For Interest And Income Taxes) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Cash Flow Information [Abstract]      
Cash payments for interest $ 586 $ 380 $ 426
Cash payments for income taxes 7,269 18,085 25,066
Proceeds from sales of assets 2,389 4,035 $ 2,707
Asset Exchange [Member]      
Asset exchanges, primarily noncash 500 $ 1,200  
Proceeds from sales of assets 100    
Capital lease obligations incurred 1,000    
Maturity Greater Than Three Months [Member]      
Net cash flow from issuance/(repayment) of commercial paper 358    
Proceeds from issuance of commercial paper 8,100    
Repayments of commercial paper $ 7,700