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Inventories
3 Months Ended
Mar. 31, 2017
Inventory Disclosure [Abstract]  
Inventories
Inventories

We value our raw materials, work in process, and finished goods inventories using lower of cost, as determined by the average cost method, or market. Supplies and materials are valued at the first-in, first-out (FIFO) or average cost methods.

The components of inventories were as follows (dollars in millions):
 
March 31,
2017
 
December 31,
2016
Raw materials
$
282.2

 
$
271.9

Work in process
13.7

 
12.9

Finished goods
212.8

 
206.5

Supplies and materials
235.8

 
232.3

Inventories
$
744.5

 
$
723.6