Inventory - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Inventory valuation reserves	$ 1.7	$ 54.0
Excess of replacement or current costs over stated LIFO value	14.9	1.5
Cost of goods sold
Lower of cost or market gains (charges)	52.3	(51.3)	$ 14.0
Effect of LIFO inventory liquidation on income	9.2	(7.5)	$ 0.9
LIFO inventory
Inventory valuation reserves	$ 1.2	$ 39.4