Inventories (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Inventory [Line Items]
Raw materials and supplies	$ 199.6		$ 199.6		$ 191.5
Work-in-process	863.5		863.5		914.1
Finished goods	180.9		180.9		191.1
Total inventories at current cost	1,244.0		1,244.0		1,296.7
Adjustment from current cost to LIFO cost basis	6.7		6.7		2.9
Inventory valuation reserves	(82.2)		(82.2)		(88.5)
Total inventories, net	1,168.5		1,168.5		1,211.1
LIFO benefit (charge)			(1.4)	$ (29.5)
NRV benefit (charge)			1.3	29.5
Net cost of sales impact	0.0	$ 0.0	(0.1)	$ 0.0
Net Realizable Value Reserve [Member]
Inventory [Line Items]
Inventory valuation reserves	(6.7)		(6.7)		$ (8.0)
Forged Products
Inventory [Line Items]
Adjustment from current cost to LIFO cost basis	$ 5.2		$ 5.2