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Inventories
 3 Months Ended
Mar. 31, 2021
Inventory Disclosure [Abstract]  
Inventories Inventories
March 31, 2021December 31, 2020
Finished goods$516 $528 
Work-in-process627 629 
Purchased raw materials271 292 
Operating supplies39 39 
Total inventories$1,453 $1,488 

At March 31, 2021 and December 31, 2020, the portion of inventories valued on a last-in, first-out (“LIFO”) basis was $472 and $458, respectively. If valued on an average-cost basis, total inventories would have been $139 and $131 higher at March 31, 2021 and December 31, 2020, respectively.