Derivative Instruments and Hedging Activities (Details 3) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) arising in period	$ (4.1)	$ (8.2)	$ (5.5)	$ (16.2)
Recorded in cost of products sold	5.5	1.3	13.1	1.9
Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) arising in period	(2.6)	(8.2)	(2.3)	(16.2)
Foreign Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) arising in period	(1.5)	0.0	(3.2)	0.0
Other Nonoperating Income (Expense) [Member] | Foreign Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as cash flow hedges:	0.7	(0.6)	0.4	(0.7)
Cost of Products Sold [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recorded in cost of products sold	5.5	1.3	13.1	1.9
Cost of Products Sold [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recorded in cost of products sold	5.4	1.3	13.0	1.9
Derivatives not designated as cash flow hedges:	2.3	(8.2)	(6.4)	7.1
Cost of Products Sold [Member] | Foreign Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Recorded in cost of products sold	0.1	0.0	0.1	0.0
Iron Ore [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Cash Received on Hedge	9.2	8.9	11.5	20.3
Iron Ore [Member] | Cost of Products Sold [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives not designated as cash flow hedges:	$ 2.1	$ (8.4)	$ (5.6)	$ 7.9