Financial Information for Subsidiary and Guarantor Parent (B.S.) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	$ 141.6	$ 229.6	$ 149.8	$ 269.5
Accounts receivable, net	545.3	452.1
Intercompany notes receivable	0.0	0.0
Inventories, net	1,176.1	1,037.0
Prepaid expenses and other current assets	52.7	47.8
Total Current Assets	1,915.7	1,766.5
Property, plant and equipment, net	2,495.7	2,498.9
Goodwill	531.4	641.9
Intercompany notes receivable	0.0	0.0
Investments in subsidiaries	0.0	0.0
Other assets	242.6	262.7
Total Assets	5,185.4	5,170.0	5,751.7
Accounts payable	420.1	294.3
Accrued liabilities	282.4	309.3
Intercompany notes payable	0.0	0.0
Short-term debt and current portion of long-term debt	10.1	105.1
Total Current Liabilities	712.6	708.7
Long-term debt	1,530.6	1,771.9
Intercompany notes payable	0.0	0.0
Accrued postretirement benefits	317.8	317.7
Pension liabilities	697.0	827.9
Deferred income taxes	9.7	15.6
Other long-term liabilities	73.2	83.4
Total Liabilities	3,340.9	3,725.2
Redeemable noncontrolling interest	0.0		12.1
Total Stockholders’ Equity	1,844.5	1,444.8	$ 2,184.4	$ 2,709.3
Total Liabilities and Stockholders’ Equity	5,185.4	5,170.0
Legal Entities [Member] | Guarantor Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	2.1	2.3
Accounts receivable, net	0.2	0.1
Intercompany notes receivable	0.0	0.0
Inventories, net	0.0	0.0
Prepaid expenses and other current assets	6.6	6.6
Total Current Assets	8.9	9.0
Property, plant and equipment, net	0.9	1.3
Goodwill	0.0	0.0
Intercompany notes receivable	0.0	0.0
Investments in subsidiaries	5,645.6	5,241.2
Other assets	25.4	23.0
Total Assets	5,680.8	5,274.5
Accounts payable	3.0	3.1
Accrued liabilities	54.1	54.6
Intercompany notes payable	1,836.5	1,341.1
Short-term debt and current portion of long-term debt	0.3	0.4
Total Current Liabilities	1,893.9	1,399.2
Long-term debt	1,275.7	1,621.7
Intercompany notes payable	0.0	0.0
Accrued postretirement benefits	0.0	0.0
Pension liabilities	644.3	778.5
Deferred income taxes	9.7	15.6
Other long-term liabilities	12.7	14.7
Total Liabilities	3,836.3	3,829.7
Total Stockholders’ Equity	1,844.5	1,444.8
Total Liabilities and Stockholders’ Equity	5,680.8	5,274.5
Legal Entities [Member] | Subsidiary [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	13.5	2.5
Accounts receivable, net	141.6	107.8
Intercompany notes receivable	0.0	0.0
Inventories, net	207.9	106.7
Prepaid expenses and other current assets	4.5	5.2
Total Current Assets	367.5	222.2
Property, plant and equipment, net	1,581.6	1,583.6
Goodwill	0.0	0.0
Intercompany notes receivable	0.0	0.0
Investments in subsidiaries	37.7	37.7
Other assets	18.0	25.5
Total Assets	2,004.8	1,869.0
Accounts payable	180.3	97.4
Accrued liabilities	88.5	83.3
Intercompany notes payable	1,669.1	1,551.8
Short-term debt and current portion of long-term debt	0.6	0.3
Total Current Liabilities	1,938.5	1,732.8
Long-term debt	150.7	150.0
Intercompany notes payable	200.0	200.0
Accrued postretirement benefits	250.2	244.0
Pension liabilities	4.4	5.2
Deferred income taxes	0.0	0.0
Other long-term liabilities	17.2	18.1
Total Liabilities	2,561.0	2,350.1
Total Stockholders’ Equity	(556.2)	(481.1)
Total Liabilities and Stockholders’ Equity	2,004.8	1,869.0
Legal Entities [Member] | Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	126.0	224.8
Accounts receivable, net	403.5	344.2
Intercompany notes receivable	3,505.6	2,892.9
Inventories, net	968.2	930.3
Prepaid expenses and other current assets	41.6	36.0
Total Current Assets	5,044.9	4,428.2
Property, plant and equipment, net	913.2	914.0
Goodwill	531.4	641.9
Intercompany notes receivable	200.0	200.0
Investments in subsidiaries	0.0	0.0
Other assets	199.2	214.2
Total Assets	6,888.7	6,398.3
Accounts payable	236.8	193.8
Accrued liabilities	139.8	171.4
Intercompany notes payable	0.0	0.0
Short-term debt and current portion of long-term debt	9.2	104.4
Total Current Liabilities	385.8	469.6
Long-term debt	104.2	0.2
Intercompany notes payable	0.0	0.0
Accrued postretirement benefits	67.6	73.7
Pension liabilities	48.3	44.2
Deferred income taxes	0.0	0.0
Other long-term liabilities	43.3	50.6
Total Liabilities	649.2	638.3
Total Stockholders’ Equity	6,239.5	5,760.0
Total Liabilities and Stockholders’ Equity	6,888.7	6,398.3
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	0.0	0.0
Accounts receivable, net	0.0	0.0
Intercompany notes receivable	(3,505.6)	(2,892.9)
Inventories, net	0.0	0.0
Prepaid expenses and other current assets	0.0	0.0
Total Current Assets	(3,505.6)	(2,892.9)
Property, plant and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Intercompany notes receivable	(200.0)	(200.0)
Investments in subsidiaries	(5,683.3)	(5,278.9)
Other assets	0.0	0.0
Total Assets	(9,388.9)	(8,371.8)
Accounts payable	0.0	0.0
Accrued liabilities	0.0	0.0
Intercompany notes payable	(3,505.6)	(2,892.9)
Short-term debt and current portion of long-term debt	0.0	0.0
Total Current Liabilities	(3,505.6)	(2,892.9)
Long-term debt	0.0	0.0
Intercompany notes payable	(200.0)	(200.0)
Accrued postretirement benefits	0.0	0.0
Pension liabilities	0.0	0.0
Deferred income taxes	0.0	0.0
Other long-term liabilities	0.0	0.0
Total Liabilities	(3,705.6)	(3,092.9)
Total Stockholders’ Equity	(5,683.3)	(5,278.9)
Total Liabilities and Stockholders’ Equity	$ (9,388.9)	$ (8,371.8)