Inventories (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Finished goods	$ 457.8	$ 353.7
Work in process	456.1	542.4
Raw materials, supplies and other	250.0	224.1
First-in, first-out inventory	1,163.9	1,120.2
Less: Excess of first-in, first-out cost over last-in, first-out cost	(128.7)	(127.7)
Net inventories	$ 1,035.2	$ 992.5