Inventories
3 Months Ended
Mar. 31, 2018
Inventory Disclosure [Abstract]  
Inventories
Inventories
(In millions)
March 31,
2018
 
December 31,
2017
Crude oil and refinery feedstocks
$
1,777

 
$
2,056

Refined products
2,746

 
2,839

Materials and supplies
435

 
494

Merchandise
153

 
161

Total
$
5,111

 
$
5,550


Inventories are carried at the lower of cost or market value. The cost of inventories of crude oil and refinery feedstocks, refined products and merchandise is determined primarily under the LIFO method. There were no material liquidations of LIFO inventories for the three months ended March 31, 2018.