SUPPLEMENTAL GUARANTOR FINANCIAL INFORMATION (Balance Sheet)(Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Supplemental Guarantor Financial Information Balance Sheets [Line Items]
Cash and cash equivalents	$ 109.1	$ 218.4	$ 168.5	$ 184.5
Receivables, net	835.6	733.2	774.5
Receivables, net	0.0	0.0	0.0
Income taxes receivable	17.5	16.9	25.5
Inventories, net	675.6	682.6	656.3
Other current assets	61.2	48.1	44.9
Total current assets	1,699.0	1,699.2	1,669.7
Property, plant and equipment, net	3,539.4	3,575.8	3,659.2
Investment in subsidiaries	0.0	0.0	0.0
Deferred income taxes	39.4	36.4	112.7
Other assets	1,197.0	1,208.4	637.2
Long-term receivables—affiliates	0.0	0.0	0.0
Intangible assets, net	565.1	578.5	615.4
Goodwill	2,120.3	2,120.0	2,119.0	2,118.0
Total assets	9,160.2	9,218.3	8,813.2
Current installments of long-term debt	0.7	0.7	81.8
Accounts payable	698.2	669.8	637.3
Intercompany payables	0.0	0.0	0.0
Income taxes payable	16.0	9.4	8.1
Accrued liabilities	256.1	274.4	258.2
Total current liabilities	971.0	954.3	985.4
Long-term debt	3,534.7	3,611.3	3,530.8
Accrued pension liability	628.7	635.9	627.5
Deferred income taxes	498.4	511.2	1,033.0
Long-term payables—affiliates	0.0	0.0	0.0
Other liabilities	764.3	751.9	364.9
Total liabilities	6,397.1	6,464.6	6,541.6
Commitments and contingencies
Common stock	167.2	167.1	165.9
Additional paid-in capital	2,285.0	2,280.9	2,253.7
Accumulated other comprehensive loss	(552.8)	(484.6)	(502.1)	(510.0)
Retained earnings	863.7	790.3	354.1
Total shareholders’ equity	2,763.1	2,753.7	2,271.6	2,273.0
Total liabilities and shareholders’ equity	9,160.2	9,218.3	8,813.2
Parent Guarantor
Supplemental Guarantor Financial Information Balance Sheets [Line Items]
Cash and cash equivalents	3.6	57.1	27.5	25.2
Receivables, net	119.6	95.6	113.6
Receivables, net	0.0	0.0	0.0
Income taxes receivable	11.4	11.7	21.7
Inventories, net	160.2	155.4	181.3
Other current assets	223.7	206.2	182.1
Total current assets	518.5	526.0	526.2
Property, plant and equipment, net	551.8	544.4	509.2
Investment in subsidiaries	6,720.1	6,680.4	6,068.3
Deferred income taxes	43.7	38.1	123.4
Other assets	47.3	45.9	50.0
Long-term receivables—affiliates	0.0	0.0	0.0
Intangible assets, net	0.3	0.3	0.4
Goodwill	0.0	0.0	0.0
Total assets	7,881.7	7,835.1	7,277.5
Current installments of long-term debt	0.7	0.7	0.8
Accounts payable	62.0	83.2	48.6
Intercompany payables	2,191.7	2,093.2	1,978.4
Income taxes payable	2.3	0.0	0.0
Accrued liabilities	115.0	117.7	130.7
Total current liabilities	2,371.7	2,294.8	2,158.5
Long-term debt	1,352.2	839.4	818.3
Accrued pension liability	391.4	406.7	437.9
Deferred income taxes	0.0	0.0	0.0
Long-term payables—affiliates	680.0	1,250.0	1,301.6
Other liabilities	323.3	290.5	289.6
Total liabilities	5,118.6	5,081.4	5,005.9
Common stock	167.2	167.1	165.9
Additional paid-in capital	2,285.0	2,280.9	2,253.7
Accumulated other comprehensive loss	(552.8)	(484.6)	(502.1)
Retained earnings	863.7	790.3	354.1
Total shareholders’ equity	2,763.1	2,753.7	2,271.6
Total liabilities and shareholders’ equity	7,881.7	7,835.1	7,277.5
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	0.0
Receivables, net	0.0	0.0	1.6
Income taxes receivable	0.0	0.0	0.7
Inventories, net	0.0	0.0	0.0
Other current assets	0.0	0.0	3.4
Total current assets	0.0	0.0	5.7
Property, plant and equipment, net	0.0	0.0	0.0
Investment in subsidiaries	4,114.5	4,092.3	3,769.8
Deferred income taxes	0.0	0.0	0.0
Other assets	0.0	0.0	0.0
Long-term receivables—affiliates	1,531.8	2,132.1	2,227.6
Intangible assets, net	5.7	5.7	5.7
Goodwill	966.3	966.3	966.3
Total assets	6,618.3	7,196.4	6,975.1
Current installments of long-term debt	0.0	0.0	68.8
Accounts payable	0.0	0.0	0.0
Intercompany payables	0.0	0.0	0.0
Income taxes payable	0.0	0.0	0.0
Accrued liabilities	0.0	0.0	0.0
Total current liabilities	0.0	0.0	68.8
Long-term debt	1,952.2	2,522.2	2,503.3
Accrued pension liability	0.0	0.0	0.0
Deferred income taxes	4.1	3.0	223.3
Long-term payables—affiliates	0.0	0.0	0.0
Other liabilities	5.6	5.6	6.5
Total liabilities	1,961.9	2,530.8	2,801.9
Common stock	0.0	0.0	0.0
Additional paid-in capital	4,125.7	4,125.7	4,125.7
Accumulated other comprehensive loss	0.0	0.0	0.0
Retained earnings	530.7	539.9	47.5
Total shareholders’ equity	4,656.4	4,665.6	4,173.2
Total liabilities and shareholders’ equity	6,618.3	7,196.4	6,975.1
Subsidiary Non-Guarantor
Supplemental Guarantor Financial Information Balance Sheets [Line Items]
Cash and cash equivalents	105.5	161.3	141.0	159.3
Receivables, net	716.0	637.6	660.9
Receivables, net	2,191.7	2,093.2	1,976.8
Income taxes receivable	6.1	6.3	6.9
Inventories, net	515.4	527.2	475.0
Other current assets	7.3	5.3	4.4
Total current assets	3,542.0	3,430.9	3,265.0
Property, plant and equipment, net	2,987.6	3,031.4	3,150.0
Investment in subsidiaries	0.0	0.0	0.0
Deferred income taxes	42.5	34.5	104.3
Other assets	1,149.7	1,162.5	587.2
Long-term receivables—affiliates	0.0	0.0	0.0
Intangible assets, net	559.1	572.5	609.3
Goodwill	1,154.0	1,153.7	1,152.7
Total assets	9,434.9	9,385.5	8,868.5
Current installments of long-term debt	0.0	0.0	12.2
Accounts payable	639.7	590.0	590.1
Intercompany payables	0.0	0.0	0.0
Income taxes payable	13.7	10.5	11.9
Accrued liabilities	308.7	318.1	272.5
Total current liabilities	962.1	918.6	886.7
Long-term debt	230.3	249.7	209.2
Accrued pension liability	237.3	229.2	189.6
Deferred income taxes	541.1	544.4	924.7
Long-term payables—affiliates	851.8	882.1	926.0
Other liabilities	435.4	455.8	68.8
Total liabilities	3,258.0	3,279.8	3,205.0
Common stock	14.6	14.6	14.6
Additional paid-in capital	4,808.2	4,808.2	4,808.2
Accumulated other comprehensive loss	(4.8)	(4.6)	(5.1)
Retained earnings	1,358.9	1,287.5	845.8
Total shareholders’ equity	6,176.9	6,105.7	5,663.5
Total liabilities and shareholders’ equity	9,434.9	9,385.5	8,868.5
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	0.0
Receivables, net	(2,191.7)	(2,093.2)	(1,978.4)
Income taxes receivable	0.0	(1.1)	(3.8)
Inventories, net	0.0	0.0	0.0
Other current assets	(169.8)	(163.4)	(145.0)
Total current assets	(2,361.5)	(2,257.7)	(2,127.2)
Property, plant and equipment, net	0.0	0.0	0.0
Investment in subsidiaries	(10,834.6)	(10,772.7)	(9,838.1)
Deferred income taxes	(46.8)	(36.2)	(115.0)
Other assets	0.0	0.0	0.0
Long-term receivables—affiliates	(1,531.8)	(2,132.1)	(2,227.6)
Intangible assets, net	0.0	0.0	0.0
Goodwill	0.0	0.0	0.0
Total assets	(14,774.7)	(15,198.7)	(14,307.9)
Current installments of long-term debt	0.0	0.0	0.0
Accounts payable	(3.5)	(3.4)	(1.4)
Intercompany payables	(2,191.7)	(2,093.2)	(1,978.4)
Income taxes payable	0.0	(1.1)	(3.8)
Accrued liabilities	(167.6)	(161.4)	(145.0)
Total current liabilities	(2,362.8)	(2,259.1)	(2,128.6)
Long-term debt	0.0	0.0	0.0
Accrued pension liability	0.0	0.0	0.0
Deferred income taxes	(46.8)	(36.2)	(115.0)
Long-term payables—affiliates	(1,531.8)	(2,132.1)	(2,227.6)
Other liabilities	0.0	0.0	0.0
Total liabilities	(3,941.4)	(4,427.4)	(4,471.2)
Common stock	(14.6)	(14.6)	(14.6)
Additional paid-in capital	(8,933.9)	(8,933.9)	(8,933.9)
Accumulated other comprehensive loss	4.8	4.6	5.1
Retained earnings	(1,889.6)	(1,827.4)	(893.3)
Total shareholders’ equity	(10,833.3)	(10,771.3)	(9,836.7)
Total liabilities and shareholders’ equity	$ (14,774.7)	$ (15,198.7)	$ (14,307.9)