Financial Information for Subsidiary and Guarantor Parent (B.S.) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
ASSETS
Cash and cash equivalents	$ 322.3	$ 149.8	$ 250.9	$ 269.5
Accounts receivable, net	492.5	400.3
Intercompany notes receivable	0.0	0.0
Inventories, net	1,094.3	1,271.6
Prepaid expenses and other current assets	43.3	45.9
Total current assets	1,952.4	1,867.6
Property, plant and equipment, net	2,958.9	2,928.2
Goodwill	646.9	651.4
Intercompany notes receivable	0.0	0.0
Investment in subsidiaries	0.0	0.0
Other assets	302.8	304.5
Total assets	5,861.0	5,751.7
LIABILITIES AND EQUITY
Accounts payable	308.2	380.8
Accrued liabilities	290.8	301.8
Intercompany notes payable	0.0	0.0
Short-term debt and current portion of long-term debt	6.7	3.9
Total current liabilities	605.7	686.5
Long-term debt	1,870.1	1,491.8
Intercompany notes payable	0.0	0.0
Accrued postretirement benefits	316.5	359.2
Pension liabilities	826.7	833.8
Deferred income taxes	52.8	75.6
Other long-term liabilities	89.9	108.3
Total liabilities	3,761.7	3,555.2
Redeemable noncontrolling interest	0.0	12.1
Total stockholders’ equity	2,099.3	2,184.4	$ 2,700.7	$ 2,709.3
Total Liabilities and Equity	5,861.0	5,751.7
Reportable Legal Entities | Parent Company
ASSETS
Cash and cash equivalents	0.4	0.4
Accounts receivable, net	0.1	0.1
Intercompany notes receivable	0.0	0.0
Inventories, net	0.0	0.0
Prepaid expenses and other current assets	12.3	9.3
Total current assets	12.8	9.8
Property, plant and equipment, net	1.7	2.2
Goodwill	0.0	0.0
Intercompany notes receivable	0.0	0.0
Investment in subsidiaries	5,814.7	5,742.5
Other assets	16.8	13.4
Total assets	5,846.0	5,767.9
LIABILITIES AND EQUITY
Accounts payable	3.8	4.8
Accrued liabilities	36.5	42.1
Intercompany notes payable	1,240.9	1,325.4
Short-term debt and current portion of long-term debt	0.7	0.7
Total current liabilities	1,281.9	1,373.0
Long-term debt	1,620.4	1,341.7
Intercompany notes payable	0.0	0.0
Accrued postretirement benefits	0.0	0.0
Pension liabilities	775.2	778.0
Deferred income taxes	52.8	75.6
Other long-term liabilities	16.4	15.2
Total liabilities	3,746.7	3,583.5
Redeemable noncontrolling interest		0.0
Total stockholders’ equity	2,099.3	2,184.4
Total Liabilities and Equity	5,846.0	5,767.9
Reportable Legal Entities | Subsidiary
ASSETS
Cash and cash equivalents	3.9	2.8
Accounts receivable, net	121.0	100.3
Intercompany notes receivable	0.0	0.0
Inventories, net	141.4	239.9
Prepaid expenses and other current assets	7.0	3.8
Total current assets	273.3	346.8
Property, plant and equipment, net	1,590.8	1,559.9
Goodwill	0.0	0.0
Intercompany notes receivable	0.0	0.0
Investment in subsidiaries	37.7	37.7
Other assets	26.4	23.0
Total assets	1,928.2	1,967.4
LIABILITIES AND EQUITY
Accounts payable	117.9	171.1
Accrued liabilities	90.6	74.0
Intercompany notes payable	1,499.4	1,276.1
Short-term debt and current portion of long-term debt	0.3	0.1
Total current liabilities	1,708.2	1,521.3
Long-term debt	150.0	149.7
Intercompany notes payable	200.0	200.0
Accrued postretirement benefits	246.8	280.0
Pension liabilities	4.8	5.2
Deferred income taxes	0.0	0.0
Other long-term liabilities	19.1	20.7
Total liabilities	2,328.9	2,176.9
Redeemable noncontrolling interest		0.0
Total stockholders’ equity	(400.7)	(209.5)
Total Liabilities and Equity	1,928.2	1,967.4
Reportable Legal Entities | NonGuarantor Subsidiaries
ASSETS
Cash and cash equivalents	318.0	146.6
Accounts receivable, net	371.4	299.9
Intercompany notes receivable	2,740.3	2,601.5
Inventories, net	952.9	1,031.7
Prepaid expenses and other current assets	24.0	32.8
Total current assets	4,406.6	4,112.5
Property, plant and equipment, net	1,366.4	1,366.1
Goodwill	646.9	651.4
Intercompany notes receivable	200.0	200.0
Investment in subsidiaries	0.0	0.0
Other assets	259.6	268.1
Total assets	6,879.5	6,598.1
LIABILITIES AND EQUITY
Accounts payable	186.5	204.9
Accrued liabilities	163.7	185.7
Intercompany notes payable	0.0	0.0
Short-term debt and current portion of long-term debt	5.7	3.1
Total current liabilities	355.9	393.7
Long-term debt	99.7	0.4
Intercompany notes payable	0.0	0.0
Accrued postretirement benefits	69.7	79.2
Pension liabilities	46.7	50.6
Deferred income taxes	0.0	0.0
Other long-term liabilities	54.4	72.4
Total liabilities	626.4	596.3
Redeemable noncontrolling interest		12.1
Total stockholders’ equity	6,253.1	5,989.7
Total Liabilities and Equity	6,879.5	6,598.1
Eliminations
ASSETS
Cash and cash equivalents	0.0	0.0
Accounts receivable, net	0.0	0.0
Intercompany notes receivable	(2,740.3)	(2,601.5)
Inventories, net	0.0	0.0
Prepaid expenses and other current assets	0.0	0.0
Total current assets	(2,740.3)	(2,601.5)
Property, plant and equipment, net	0.0	0.0
Goodwill	0.0	0.0
Intercompany notes receivable	(200.0)	(200.0)
Investment in subsidiaries	(5,852.4)	(5,780.2)
Other assets	0.0	0.0
Total assets	(8,792.7)	(8,581.7)
LIABILITIES AND EQUITY
Accounts payable	0.0	0.0
Accrued liabilities	0.0	0.0
Intercompany notes payable	(2,740.3)	(2,601.5)
Short-term debt and current portion of long-term debt	0.0	0.0
Total current liabilities	(2,740.3)	(2,601.5)
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	(2,940.3)	(2,801.5)
Redeemable noncontrolling interest		0.0
Total stockholders’ equity	(5,852.4)	(5,780.2)
Total Liabilities and Equity	$ (8,792.7)	$ (8,581.7)