Inventories (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Inventory [Line Items]
Raw materials and supplies	$ 175.7			$ 162.8
Work-in-process	931.8			955.5
Finished goods	181.2			165.0
Total inventories at current cost	1,288.7			1,283.3
Adjustment from current cost to LIFO cost basis	23.1			43.1
Inventory valuation reserves	(101.0)			(121.5)
Progress payments	0.0			(28.8)
Total inventories, net	1,210.8			$ 1,176.1
LIFO benefit (charge)	(8.2)	$ (8.1)
NRV benefit (charge)	8.2	8.1
Net cost of sales impact	0.0	$ 0.0
ASU 2014-09
Inventory [Line Items]
Inventory valuation reserves			$ 11.8
Total inventories, net	$ 23.5		$ 28.8