SUPPLEMENTAL GUARANTOR FINANCIAL INFORMATION (Balance Sheet) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Supplemental Guarantor Financial Information Balance Sheets [Line Items]
Cash and cash equivalents	$ 194.5	$ 220.9	$ 105.7	$ 178.8
Receivables, net	802.9	760.4	808.3
Intercompany receivables	0.0	0.0	0.0
Income taxes receivable	19.9	13.9	6.3
Inventories, net	667.5	695.7	717.5
Other current assets	54.5	23.1	46.7
Total current assets	1,739.3	1,714.0	1,684.5
Property, plant and equipment, net	3,282.7	3,323.8	3,433.5
Operating lease assets, net	366.5	377.8	275.1
Investment in subsidiaries	0.0	0.0	0.0
Deferred income taxes	39.6	35.3	31.7
Other assets	1,205.3	1,169.1	1,131.4
Long-term receivables—affiliates	0.0	0.0	0.0
Intangible assets, net	431.4	448.1	494.2
Goodwill	2,119.6	2,119.7	2,119.5	2,119.6
Total assets	9,184.4	9,187.8	9,169.9
Current installments of long-term debt	2.0	2.1	126.1
Accounts payable	668.1	651.9	637.0
Intercompany payables	0.0	0.0	0.0
Income taxes payable	7.4	19.8	13.0
Current operating lease liabilities	76.6	79.3	69.4
Accrued liabilities	811.8	329.1	294.4
Total current liabilities	1,565.9	1,082.2	1,139.9
Long-term debt	3,489.5	3,338.7	3,067.2
Operating lease liabilities	295.0	303.4	206.0
Accrued pension liability	778.0	797.7	660.2
Deferred income taxes	449.9	454.5	525.9
Long-term payables—affiliates	0.0	0.0	0.0
Other liabilities	317.0	793.8	733.1
Total liabilities	6,895.3	6,770.3	6,332.3
Commitments and contingencies
Common stock	157.8	157.7	164.9
Additional paid-in capital	2,122.8	2,122.1	2,239.2
Accumulated other comprehensive loss	(821.1)	(803.4)	(656.9)	(651.0)
Retained earnings	829.6	941.1	1,090.4
Total shareholders’ equity	2,289.1	2,417.5	2,837.6	2,832.2
Total liabilities and shareholders’ equity	9,184.4	9,187.8	9,169.9
Parent Guarantor
Supplemental Guarantor Financial Information Balance Sheets [Line Items]
Cash and cash equivalents	109.7	11.6	6.0	92.0
Receivables, net	64.3	78.3	99.0
Intercompany receivables	0.0	0.0	0.0
Income taxes receivable	9.7	1.6	0.3
Inventories, net	141.0	157.1	172.3
Other current assets	262.4	231.4	235.7
Total current assets	587.1	480.0	513.3
Property, plant and equipment, net	707.4	699.0	674.0
Operating lease assets, net	45.4	47.4	48.9
Investment in subsidiaries	7,035.4	7,048.2	7,024.5
Deferred income taxes	23.6	1.7	3.2
Other assets	19.3	20.9	17.0
Long-term receivables—affiliates	73.4	73.4	0.0
Intangible assets, net	0.3	0.3	0.3
Goodwill	0.0	0.0	0.0
Total assets	8,491.9	8,370.9	8,281.2
Current installments of long-term debt	2.0	2.1	1.1
Accounts payable	2.4	0.0	75.8
Intercompany payables	3,080.9	2,815.5	2,664.7
Income taxes payable	0.1	11.5	3.7
Current operating lease liabilities	8.2	8.2	8.0
Accrued liabilities	193.9	183.7	138.3
Total current liabilities	3,287.5	3,021.0	2,891.6
Long-term debt	2,130.8	2,130.0	1,370.3
Operating lease liabilities	38.4	40.4	42.0
Accrued pension liability	480.1	496.9	427.0
Deferred income taxes	0.0	0.0	0.0
Long-term payables—affiliates	0.0	0.0	419.6
Other liabilities	266.0	265.1	293.1
Total liabilities	6,202.8	5,953.4	5,443.6
Commitments and contingencies
Common stock	157.8	157.7	164.9
Additional paid-in capital	2,122.8	2,122.1	2,239.2
Accumulated other comprehensive loss	(821.1)	(803.4)	(656.9)
Retained earnings	829.6	941.1	1,090.4
Total shareholders’ equity	2,289.1	2,417.5	2,837.6
Total liabilities and shareholders’ equity	8,491.9	8,370.9	8,281.2
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	0.0
Intercompany receivables	0.0	0.0	0.0
Income taxes receivable	0.0	0.0	0.0
Inventories, net	0.0	0.0	0.0
Other current assets	0.0	0.0	0.0
Total current assets	0.0	0.0	0.0
Property, plant and equipment, net	0.0	0.0	0.0
Operating lease assets, net	0.0	0.0	0.0
Investment in subsidiaries	4,322.4	4,353.5	4,339.5
Deferred income taxes	0.0	0.0	0.0
Other assets	0.0	0.0	0.0
Long-term receivables—affiliates	583.1	605.8	1,169.9
Intangible assets, net	0.0	0.0	0.0
Goodwill	966.3	966.3	966.3
Total assets	5,871.8	5,925.6	6,475.7
Current installments of long-term debt	0.0	0.0	0.0
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
Current operating lease liabilities	0.0	0.0	0.0
Accrued liabilities	0.0	0.0	0.0
Total current liabilities	0.0	0.0	0.0
Long-term debt	1,209.2	1,208.7	1,696.9
Operating lease liabilities	0.0	0.0	0.0
Accrued pension liability	0.0	0.0	0.0
Deferred income taxes	6.6	6.5	6.1
Long-term payables—affiliates	0.0	0.0	0.0
Other liabilities	5.6	5.6	5.5
Total liabilities	1,221.4	1,220.8	1,708.5
Commitments and contingencies
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	524.7	579.1	641.5
Total shareholders’ equity	4,650.4	4,704.8	4,767.2
Total liabilities and shareholders’ equity	5,871.8	5,925.6	6,475.7
Subsidiary Non-Guarantor
Supplemental Guarantor Financial Information Balance Sheets [Line Items]
Cash and cash equivalents	84.8	209.3	99.7	86.8
Receivables, net	738.6	686.8	709.3
Intercompany receivables	3,080.9	2,815.5	2,664.7
Income taxes receivable	10.2	12.3	6.0
Inventories, net	526.5	538.6	545.2
Other current assets	6.7	0.2	3.5
Total current assets	4,447.7	4,262.7	4,028.4
Property, plant and equipment, net	2,575.3	2,624.8	2,759.5
Operating lease assets, net	321.1	330.4	226.2
Investment in subsidiaries	0.0	0.0	0.0
Deferred income taxes	39.9	34.7	31.9
Other assets	1,186.0	1,148.2	1,114.4
Long-term receivables—affiliates	0.0	0.0	0.0
Intangible assets, net	431.1	447.8	493.9
Goodwill	1,153.3	1,153.4	1,153.2
Total assets	10,154.4	10,002.0	9,807.5
Current installments of long-term debt	0.0	0.0	125.0
Accounts payable	672.3	660.6	566.8
Intercompany payables	0.0	0.0	0.0
Income taxes payable	7.3	8.3	9.3
Current operating lease liabilities	68.4	71.1	61.4
Accrued liabilities	829.3	350.8	345.9
Total current liabilities	1,577.3	1,090.8	1,108.4
Long-term debt	149.5	0.0	0.0
Operating lease liabilities	256.6	263.0	164.0
Accrued pension liability	297.9	300.8	233.2
Deferred income taxes	467.3	449.2	523.2
Long-term payables—affiliates	656.5	679.2	750.3
Other liabilities	45.4	523.1	434.5
Total liabilities	3,450.5	3,306.1	3,213.6
Commitments and contingencies
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	(13.6)	(6.5)	(8.1)
Retained earnings	1,894.7	1,879.6	1,779.2
Total shareholders’ equity	6,703.9	6,695.9	6,593.9
Total liabilities and shareholders’ equity	10,154.4	10,002.0	9,807.5
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	(4.7)	0.0
Intercompany receivables	(3,080.9)	(2,815.5)	(2,664.7)
Income taxes receivable	0.0	0.0	0.0
Inventories, net	0.0	0.0	0.0
Other current assets	(214.6)	(208.5)	(192.5)
Total current assets	(3,295.5)	(3,028.7)	(2,857.2)
Property, plant and equipment, net	0.0	0.0	0.0
Operating lease assets, net	0.0	0.0	0.0
Investment in subsidiaries	(11,357.8)	(11,401.7)	(11,364.0)
Deferred income taxes	(23.9)	(1.1)	(3.4)
Other assets	0.0	0.0	0.0
Long-term receivables—affiliates	(656.5)	(679.2)	(1,169.9)
Intangible assets, net	0.0	0.0	0.0
Goodwill	0.0	0.0	0.0
Total assets	(15,333.7)	(15,110.7)	(15,394.5)
Current installments of long-term debt	0.0	0.0	0.0
Accounts payable	(6.6)	(8.7)	(5.6)
Intercompany payables	(3,080.9)	(2,815.5)	(2,664.7)
Income taxes payable	0.0	0.0	0.0
Current operating lease liabilities	0.0	0.0	0.0
Accrued liabilities	(211.4)	(205.4)	(189.8)
Total current liabilities	(3,298.9)	(3,029.6)	(2,860.1)
Long-term debt	0.0	0.0	0.0
Operating lease liabilities	0.0	0.0	0.0
Accrued pension liability	0.0	0.0	0.0
Deferred income taxes	(24.0)	(1.2)	(3.4)
Long-term payables—affiliates	(656.5)	(679.2)	(1,169.9)
Other liabilities	0.0	0.0	0.0
Total liabilities	(3,979.4)	(3,710.0)	(4,033.4)
Commitments and contingencies
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	13.6	6.5	8.1
Retained earnings	(2,419.4)	(2,458.7)	(2,420.7)
Total shareholders’ equity	(11,354.3)	(11,400.7)	(11,361.1)
Total liabilities and shareholders’ equity	$ (15,333.7)	$ (15,110.7)	$ (15,394.5)