8.	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,		December 31,
	2018		2017
Raw materials	$	293.9	$	279.8
Work in process		14.4		12.6
Finished goods		202.2		217.0
Supplies and materials		255.9		253.1
Inventories	$	766.4	$	762.5