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Inventories
9 Months Ended
Sep. 30, 2016
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):
 
September 30,
2016
 
December 31,
2015
Raw materials
$
259.8

 
$
260.6

Work in process
14.9

 
14.2

Finished goods
188.0

 
189.7

Supplies and materials
227.9

 
212.3

Inventories
$
690.6

 
$
676.8