Condensed Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Sales	$ 2,221.3	$ 1,241.2	$ 4,140.1	$ 2,666.3
Operating expenses:
Cost of goods sold	1,712.2	1,235.7	3,136.0	2,609.9
Selling and administration	100.6	99.7	207.5	196.4
Restructuring charges	14.0	1.7	20.9	3.4
Other operating income	0.5	0.1	0.5	0.1
Operating income (loss)	395.0	(95.8)	776.2	(143.3)
Interest expense	65.9	69.4	150.4	132.5
Interest income	0.0	0.2	0.1	0.3
Non-operating pension income	(8.2)	(4.9)	(17.5)	(9.5)
Income (loss) before taxes	337.3	(160.1)	643.4	(266.0)
Income tax (benefit) provision	(18.5)	(40.0)	44.0	(65.9)
Net income (loss)	$ 355.8	$ (120.1)	$ 599.4	$ (200.1)
Net income (loss) per common share:
Basic	$ 2.23	$ (0.76)	$ 3.77	$ (1.27)
Diluted	$ 2.17	$ (0.76)	$ 3.69	$ (1.27)
Average common shares outstanding:
Basic	159.9	157.9	159.2	157.8
Diluted	163.8	157.9	162.3	157.8