SUPPLEMENTAL GUARANTOR FINANCIAL INFORMATION (Balance Sheet)(Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Guarantor Financial Information Balance Sheets [Line Items]
Cash and cash equivalents	$ 218.4	$ 184.5	$ 392.0	$ 256.8
Receivables, net	733.2	675.0
Intercompany receivables	0.0	0.0
Income taxes receivable	16.9	25.5
Inventories, net	682.6	630.4
Other current assets	48.1	30.8
Total current assets	1,699.2	1,546.2
Property, plant and equipment, net	3,575.8	3,704.9
Investment in subsidiaries	0.0	0.0
Deferred income taxes	36.4	119.5
Other assets	1,208.4	644.4
Long-term receivables—affiliates	0.0	0.0
Intangible assets, net	578.5	629.6
Goodwill	2,120.0	2,118.0	2,174.1
Total assets	9,218.3	8,762.6
Current installments of long-term debt	0.7	80.5
Accounts payable	669.8	570.8
Intercompany payables	0.0	0.0
Income taxes payable	9.4	7.5
Accrued liabilities	274.4	263.8
Total current liabilities	954.3	922.6
Long-term debt	3,611.3	3,537.1
Accrued pension liability	635.9	638.1
Deferred Income Tax Liabilities, Net	511.2	1,032.5
Long-term payables—affiliates	0.0	0.0
Other liabilities	751.9	359.3
Total liabilities	6,464.6	6,489.6
Commitments and contingencies
Common stock	167.1	165.4
Additional paid-in capital	2,280.9	2,243.8
Accumulated other comprehensive loss	(484.6)	(510.0)	(492.5)	(443.1)
Retained earnings	790.3	373.8
Total shareholders' equity	2,753.7	2,273.0	2,418.8	1,013.3
Total liabilities and shareholders' equity	9,218.3	8,762.6
Parent Guarantor
Supplemental Guarantor Financial Information Balance Sheets [Line Items]
Cash and cash equivalents	57.1	25.2	119.4	239.4
Receivables, net	95.6	88.3
Intercompany receivables	0.0	0.0
Income taxes receivable	11.7	19.0
Inventories, net	155.4	167.7
Other current assets	206.2	164.7
Total current assets	526.0	464.9
Property, plant and equipment, net	544.4	510.1
Investment in subsidiaries	6,680.4	6,035.2
Deferred income taxes	38.1	133.5
Other assets	45.9	48.1
Long-term receivables—affiliates	0.0	0.0
Intangible assets, net	0.3	0.4
Goodwill	0.0	0.0
Total assets	7,835.1	7,192.2
Current installments of long-term debt	0.7	0.6
Accounts payable	83.2	45.3
Intercompany payables	2,093.2	1,882.8
Income taxes payable	0.0	0.0
Accrued liabilities	117.7	124.9
Total current liabilities	2,294.8	2,053.6
Long-term debt	839.4	913.9
Accrued pension liability	406.7	453.7
Deferred Income Tax Liabilities, Net	0.0	0.0
Long-term payables—affiliates	1,250.0	1,209.1
Other liabilities	290.5	288.9
Total liabilities	5,081.4	4,919.2
Commitments and contingencies
Common stock	167.1	165.4
Additional paid-in capital	2,280.9	2,243.8
Accumulated other comprehensive loss	(484.6)	(510.0)
Retained earnings	790.3	373.8
Total shareholders' equity	2,753.7	2,273.0
Total liabilities and shareholders' equity	7,835.1	7,192.2
Issuer
Supplemental Guarantor Financial Information Balance Sheets [Line Items]
Cash and cash equivalents	0.0	0.0	0.0	0.0
Receivables, net	0.0	0.0
Intercompany receivables	0.0	0.0
Income taxes receivable	0.0	0.0
Inventories, net	0.0	0.0
Other current assets	0.0	3.4
Total current assets	0.0	3.4
Property, plant and equipment, net	0.0	0.0
Investment in subsidiaries	4,092.3	3,734.7
Deferred income taxes	0.0	0.0
Other assets	0.0	0.0
Long-term receivables—affiliates	2,132.1	2,194.2
Intangible assets, net	5.7	5.7
Goodwill	966.3	966.3
Total assets	7,196.4	6,904.3
Current installments of long-term debt	0.0	67.5
Accounts payable	0.0	0.0
Intercompany payables	0.0	29.5
Income taxes payable	0.0	0.0
Accrued liabilities	0.0	0.0
Total current liabilities	0.0	97.0
Long-term debt	2,522.2	2,413.3
Accrued pension liability	0.0	0.0
Deferred Income Tax Liabilities, Net	3.0	223.6
Long-term payables—affiliates	0.0	0.0
Other liabilities	5.6	6.6
Total liabilities	2,530.8	2,740.5
Commitments and contingencies
Common stock	0.0	0.0
Additional paid-in capital	4,125.7	4,125.7
Accumulated other comprehensive loss	0.0	0.0
Retained earnings	539.9	38.1
Total shareholders' equity	4,665.6	4,163.8
Total liabilities and shareholders' equity	7,196.4	6,904.3
Subsidiary Non-Guarantor
Supplemental Guarantor Financial Information Balance Sheets [Line Items]
Cash and cash equivalents	161.3	159.3	272.6	17.4
Receivables, net	637.6	586.7
Intercompany receivables	2,093.2	1,912.3
Income taxes receivable	6.3	7.3
Inventories, net	527.2	462.7
Other current assets	5.3	1.2
Total current assets	3,430.9	3,129.5
Property, plant and equipment, net	3,031.4	3,194.8
Investment in subsidiaries	0.0	0.0
Deferred income taxes	34.5	103.5
Other assets	1,162.5	596.3
Long-term receivables—affiliates	0.0	0.0
Intangible assets, net	572.5	623.5
Goodwill	1,153.7	1,151.7
Total assets	9,385.5	8,799.3
Current installments of long-term debt	0.0	12.4
Accounts payable	590.0	527.4
Intercompany payables	0.0	0.0
Income taxes payable	10.5	8.3
Accrued liabilities	318.1	277.5
Total current liabilities	918.6	825.6
Long-term debt	249.7	209.9
Accrued pension liability	229.2	184.4
Deferred Income Tax Liabilities, Net	544.4	926.4
Long-term payables—affiliates	882.1	985.1
Other liabilities	455.8	63.8
Total liabilities	3,279.8	3,195.2
Commitments and contingencies
Common stock	14.6	14.6
Additional paid-in capital	4,808.2	4,808.2
Accumulated other comprehensive loss	(4.6)	(7.0)
Retained earnings	1,287.5	788.3
Total shareholders' equity	6,105.7	5,604.1
Total liabilities and shareholders' equity	9,385.5	8,799.3
Eliminations
Supplemental Guarantor Financial Information Balance Sheets [Line Items]
Cash and cash equivalents	0.0	0.0	$ 0.0	$ 0.0
Receivables, net	0.0	0.0
Intercompany receivables	(2,093.2)	(1,912.3)
Income taxes receivable	(1.1)	(0.8)
Inventories, net	0.0	0.0
Other current assets	(163.4)	(138.5)
Total current assets	(2,257.7)	(2,051.6)
Property, plant and equipment, net	0.0	0.0
Investment in subsidiaries	(10,772.7)	(9,769.9)
Deferred income taxes	(36.2)	(117.5)
Other assets	0.0	0.0
Long-term receivables—affiliates	(2,132.1)	(2,194.2)
Intangible assets, net	0.0	0.0
Goodwill	0.0	0.0
Total assets	(15,198.7)	(14,133.2)
Current installments of long-term debt	0.0	0.0
Accounts payable	(3.4)	(1.9)
Intercompany payables	(2,093.2)	(1,912.3)
Income taxes payable	(1.1)	(0.8)
Accrued liabilities	(161.4)	(138.6)
Total current liabilities	(2,259.1)	(2,053.6)
Long-term debt	0.0	0.0
Accrued pension liability	0.0	0.0
Deferred Income Tax Liabilities, Net	(36.2)	(117.5)
Long-term payables—affiliates	(2,132.1)	(2,194.2)
Other liabilities	0.0	0.0
Total liabilities	(4,427.4)	(4,365.3)
Commitments and contingencies
Common stock	(14.6)	(14.6)
Additional paid-in capital	(8,933.9)	(8,933.9)
Accumulated other comprehensive loss	4.6	7.0
Retained earnings	(1,827.4)	(826.4)
Total shareholders' equity	(10,771.3)	(9,767.9)
Total liabilities and shareholders' equity	$ (15,198.7)	$ (14,133.2)