SUPPLEMENTAL GUARANTOR FINANCIAL INFORMATION (Statements of Operations) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended		51 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020
Supplemental Guarantor Financial Information Statement of Operations [Line Items]
Sales	$ 1,241.2		$ 1,592.9		$ 2,666.3	$ 3,146.3
Operating expenses:
Cost of goods sold	1,235.7		1,463.7		2,609.9	2,811.0
Selling and administration	99.7		97.0		196.4	204.0
Restructuring charges	1.7	$ 1.7	3.8	$ 4.0	3.4	7.8	$ 243.7
Other operating income (expense)	0.1		0.1		0.1	0.2
Operating (loss) income	95.8		(28.5)		143.3	(123.7)
Equity (loss) income in subsidiaries	0.0		0.0		0.0	0.0
Interest expense	69.4		57.9		132.5	115.3
Interest income	0.2		0.3		0.3	0.5
Non-operating pension income (expense)	4.9		4.2		9.5	8.1
Other income	0.0		0.0		0.0	11.2
Income (loss) before taxes	(160.1)		(24.9)		(266.0)	28.2
Income tax (benefit) provision	(40.0)		(4.9)		(65.9)	6.5
Net (loss) income	(120.1)	$ (80.0)	(20.0)	$ 41.7	(200.1)	21.7
Parent Guarantor
Supplemental Guarantor Financial Information Statement of Operations [Line Items]
Sales	346.9		324.0		700.2	656.8
Operating expenses:
Cost of goods sold	319.5		309.8		653.1	613.9
Selling and administration	69.0		47.8		108.9	99.6
Restructuring charges	0.0		0.0		0.0	1.4
Other operating income (expense)	0.1		(2.3)		0.1	(4.4)
Operating (loss) income	41.5		35.9		61.7	62.5
Equity (loss) income in subsidiaries	(65.6)		10.9		(114.1)	73.5
Interest expense	39.3		18.3		71.7	35.7
Interest income	1.3		2.0		3.4	2.6
Non-operating pension income (expense)	6.6		5.7		13.1	11.1
Other income						11.2
Income (loss) before taxes	(138.5)		(35.6)		(231.0)	0.2
Income tax (benefit) provision	(18.4)		(15.6)		(30.9)	(21.5)
Net (loss) income	(120.1)		(20.0)		(200.1)	21.7
Issuer
Supplemental Guarantor Financial Information Statement of Operations [Line Items]
Sales	0.0		0.0		0.0	0.0
Operating expenses:
Cost of goods sold	0.0		0.0		0.0	0.0
Selling and administration	0.0		0.0		0.0	0.0
Restructuring charges	0.0		0.0		0.0	0.0
Other operating income (expense)	0.0		0.0		0.0	0.0
Operating (loss) income	0.0		0.0		0.0	0.0
Equity (loss) income in subsidiaries	(59.5)		(8.6)		(90.6)	44.0
Interest expense	30.6		35.7		61.2	71.8
Interest income	0.0		0.0		0.0	0.0
Non-operating pension income (expense)	0.0		0.0		0.0	0.0
Other income						0.0
Income (loss) before taxes	(90.1)		(44.3)		(151.8)	(27.8)
Income tax (benefit) provision	(7.2)		(8.7)		(14.5)	(17.4)
Net (loss) income	(82.9)		(35.6)		(137.3)	(10.4)
Subsidiary Non-Guarantor
Supplemental Guarantor Financial Information Statement of Operations [Line Items]
Sales	1,023.8		1,397.3		2,225.6	2,725.0
Operating expenses:
Cost of goods sold	1,045.7		1,282.3		2,216.3	2,432.6
Selling and administration	30.7		49.2		87.5	104.4
Restructuring charges	1.7		3.8		3.4	6.4
Other operating income (expense)	0.0		2.4		0.0	4.6
Operating (loss) income	54.3		(64.4)		81.6	(186.2)
Equity (loss) income in subsidiaries	0.0		0.0		0.0	0.0
Interest expense	0.6		6.5		3.7	11.7
Interest income	0.0		0.9		1.0	1.8
Non-operating pension income (expense)	(1.7)		(1.5)		(3.6)	(3.0)
Other income						0.0
Income (loss) before taxes	(56.6)		57.3		(87.9)	173.3
Income tax (benefit) provision	(14.4)		19.4		(20.5)	45.4
Net (loss) income	(42.2)		37.9		(67.4)	127.9
Eliminations
Supplemental Guarantor Financial Information Statement of Operations [Line Items]
Sales	(129.5)		(128.4)		(259.5)	(235.5)
Operating expenses:
Cost of goods sold	(129.5)		(128.4)		(259.5)	(235.5)
Selling and administration	0.0		0.0		0.0	0.0
Restructuring charges	0.0		0.0		0.0	0.0
Other operating income (expense)	0.0		0.0		0.0	0.0
Operating (loss) income	0.0		0.0		0.0	0.0
Equity (loss) income in subsidiaries	125.1		(2.3)		204.7	(117.5)
Interest expense	(1.1)		(2.6)		(4.1)	(3.9)
Interest income	(1.1)		(2.6)		(4.1)	(3.9)
Non-operating pension income (expense)	0.0		0.0		0.0	0.0
Other income						0.0
Income (loss) before taxes	125.1		(2.3)		204.7	(117.5)
Income tax (benefit) provision	0.0		0.0		0.0	0.0
Net (loss) income	$ 125.1		$ (2.3)		$ 204.7	$ (117.5)