Condensed Guarantor and Non-Guarantor Financial Information, Balance Sheets (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Current assets:
Cash and cash equivalents	$ 57.1	$ 55.2	$ 195.3
Short-term investments	175.7	231.0
Receivables:
Trade receivables, net	145.6	137.7
Intercompany receivables	0.0	0.0
Other	10.7	11.9
Inventories	199.9	201.6
Prepaid expenses and other current assets	26.8	18.5
Total current assets	615.8	655.9
Investments in and advances to subsidiaries	0.0	0.0
Property, plant and equipment, net	552.1	530.9
Long-term intercompany loans receivable	0.0	0.0
Deferred tax assets, net	138.3	159.7
Intangible assets, net	25.7	26.4
Goodwill	18.8	37.2
Other assets	36.0	33.4
Total	1,386.7	1,443.5
Current liabilities:
Accounts payable	84.2	75.8
Intercompany loans payable	0.0	0.0
Accrued salaries, wages and related expenses	34.6	49.1
Other accrued liabilities	37.5	40.1
Total current liabilities	156.3	165.0
Net liabilities of Salaried VEBA	28.0	28.6
Deferred tax liabilities	3.3	3.3
Long-term intercompany loans payable	0.0	0.0
Long-term liabilities	61.1	73.2
Long-term debt	369.2	368.7
Total liabilities	617.9	638.8
Total stockholders' equity	768.8	804.7
Total	1,386.7	1,443.5
Consolidating Adjustments
Current assets:
Cash and cash equivalents	0.0	0.0
Short-term investments	0.0	0.0
Receivables:
Trade receivables, net	0.0	0.0
Intercompany receivables	(67.7)	(86.5)
Other	0.0	0.0
Inventories	(4.5)	(3.9)
Prepaid expenses and other current assets	0.0	(0.5)
Total current assets	(72.2)	(90.9)
Investments in and advances to subsidiaries	(1,116.8)	(1,052.5)
Property, plant and equipment, net	0.0	0.0
Long-term intercompany loans receivable	(2.7)	(85.1)
Deferred tax assets, net	4.8	4.8
Intangible assets, net	0.0	0.0
Goodwill	0.0	0.0
Other assets	0.0	0.0
Total	(1,186.9)	(1,223.7)
Current liabilities:
Accounts payable	0.0	0.0
Intercompany loans payable	(67.7)	(86.5)
Accrued salaries, wages and related expenses	0.0	0.0
Other accrued liabilities	(4.7)	(14.7)
Total current liabilities	(72.4)	(101.2)
Net liabilities of Salaried VEBA	0.0	0.0
Deferred tax liabilities	0.0	0.0
Long-term intercompany loans payable	(2.7)	(85.1)
Long-term liabilities	0.0	0.0
Long-term debt	0.0	0.0
Total liabilities	(75.1)	(186.3)
Total stockholders' equity	(1,111.8)	(1,037.4)
Total	(1,186.9)	(1,223.7)
Parent
Current assets:
Cash and cash equivalents	0.0	0.0
Short-term investments	0.0	0.0
Receivables:
Trade receivables, net	0.0	0.0
Intercompany receivables	66.9	85.8
Other	0.0	0.0
Inventories	0.0	0.0
Prepaid expenses and other current assets	0.2	0.1
Total current assets	67.1	85.9
Investments in and advances to subsidiaries	1,075.5	1,012.4
Property, plant and equipment, net	0.0	0.0
Long-term intercompany loans receivable	0.0	80.2
Deferred tax assets, net	0.0	0.0
Intangible assets, net	0.0	0.0
Goodwill	0.0	0.0
Other assets	0.0	0.0
Total	1,142.6	1,178.5
Current liabilities:
Accounts payable	1.8	2.2
Intercompany loans payable	0.0	0.0
Accrued salaries, wages and related expenses	0.0	0.0
Other accrued liabilities	2.8	2.9
Total current liabilities	4.6	5.1
Net liabilities of Salaried VEBA	0.0	0.0
Deferred tax liabilities	0.0	0.0
Long-term intercompany loans payable	0.0	0.0
Long-term liabilities	0.0	0.0
Long-term debt	369.2	368.7
Total liabilities	373.8	373.8
Total stockholders' equity	768.8	804.7
Total	1,142.6	1,178.5
Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	49.9	52.9
Short-term investments	175.7	231.0
Receivables:
Trade receivables, net	139.0	133.1
Intercompany receivables	0.2	0.1
Other	10.0	11.4
Inventories	196.7	197.5
Prepaid expenses and other current assets	26.3	18.0
Total current assets	597.8	644.0
Investments in and advances to subsidiaries	41.3	40.1
Property, plant and equipment, net	521.6	499.5
Long-term intercompany loans receivable	0.0	0.0
Deferred tax assets, net	133.5	154.9
Intangible assets, net	25.7	26.4
Goodwill	18.8	37.2
Other assets	36.0	33.4
Total	1,374.7	1,435.5
Current liabilities:
Accounts payable	77.0	68.9
Intercompany loans payable	67.6	86.4
Accrued salaries, wages and related expenses	33.1	47.2
Other accrued liabilities	39.3	52.6
Total current liabilities	217.0	255.1
Net liabilities of Salaried VEBA	28.0	28.6
Deferred tax liabilities	0.0	0.0
Long-term intercompany loans payable	2.7	85.1
Long-term liabilities	58.5	70.5
Long-term debt	0.0	0.0
Total liabilities	306.2	439.3
Total stockholders' equity	1,068.5	996.2
Total	1,374.7	1,435.5
Non-Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	7.2	2.3
Short-term investments	0.0	0.0
Receivables:
Trade receivables, net	6.6	4.6
Intercompany receivables	0.6	0.6
Other	0.7	0.5
Inventories	7.7	8.0
Prepaid expenses and other current assets	0.3	0.9
Total current assets	23.1	16.9
Investments in and advances to subsidiaries	0.0	0.0
Property, plant and equipment, net	30.5	31.4
Long-term intercompany loans receivable	2.7	4.9
Deferred tax assets, net	0.0	0.0
Intangible assets, net	0.0	0.0
Goodwill	0.0	0.0
Other assets	0.0	0.0
Total	56.3	53.2
Current liabilities:
Accounts payable	5.4	4.7
Intercompany loans payable	0.1	0.1
Accrued salaries, wages and related expenses	1.5	1.9
Other accrued liabilities	0.1	(0.7)
Total current liabilities	7.1	6.0
Net liabilities of Salaried VEBA	0.0	0.0
Deferred tax liabilities	3.3	3.3
Long-term intercompany loans payable	0.0	0.0
Long-term liabilities	2.6	2.7
Long-term debt	0.0	0.0
Total liabilities	13.0	12.0
Total stockholders' equity	43.3	41.2
Total	$ 56.3	$ 53.2