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Inventories (Tables)
12 Months Ended
Dec. 31, 2016
Inventory Disclosure [Abstract]  
Summary of inventories
Inventories at December 31 consisted of the following:
 
 
Millions of Dollars
 
2016

 
2015

 
 
 
 
Crude oil and petroleum products
$
2,883

 
3,214

Materials and supplies
267

 
263

 
$
3,150

 
3,477