SUPPLEMENTAL GUARANTOR FINANCIAL INFORMATION (Cash Flows)(Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Guarantor Financial Information Statements Of Cash Flows [Line Items]
Net cash provided by (used for) operating activities	$ 907.8	$ 648.8	$ 603.2
Capital expenditures	(385.2)	(294.3)	(278.0)
Business acquired and related transactions, net of cash acquired	0.0	0.0	(69.5)
Payments under long-term supply contracts	0.0	(209.4)	(175.7)
Proceeds from sale/leaseback of equipment	0.0		40.4
Proceeds from disposition of property, plant and equipment	2.9	5.2	0.5
Proceeds from disposition of affiliated companies	0.0	0.0	8.8
Distributions from consolidated subsidiaries, net	0.0	0.0
Net investing activities	(382.3)	(498.5)	(473.5)
Long-term debt:
Borrowings	570.0	2,035.5	230.0
Repayments	(946.1)	(2,037.9)	(435.3)
Common stock repurchased and retired	(50.0)	0.0	0.0
Stock options exercised	3.4	29.8	0.5
Excess tax benefits from stock-based compensation	0.0	0.0	0.4
Dividends paid	(133.6)	(133.0)	(132.1)
Debt issuance costs	(8.5)	(11.2)	(1.0)
Intercompany financing activities	0.0	0.0	0.0
Net financing activities	(564.8)	(116.8)	(337.5)
Effect of exchange rate changes on cash and cash equivalents	(0.3)	0.4	0.3
Net (decrease) increase in cash and cash equivalents	(39.6)	33.9	(207.5)
Cash and cash equivalents, beginning of year	218.4	184.5	392.0
Cash and cash equivalents, end of year	178.8	218.4	184.5
Parent Guarantor
Supplemental Guarantor Financial Information Statements Of Cash Flows [Line Items]
Net cash provided by (used for) operating activities	529.8	472.0	702.6
Capital expenditures	(149.8)	(89.1)	(65.7)
Business acquired and related transactions, net of cash acquired			(69.5)
Payments under long-term supply contracts		0.0	0.0
Proceeds from sale/leaseback of equipment			0.0
Proceeds from disposition of property, plant and equipment	0.0	0.0	0.2
Proceeds from disposition of affiliated companies			8.8
Distributions from consolidated subsidiaries, net	95.0	2.7
Net investing activities	(54.8)	(86.4)	(126.2)
Long-term debt:
Borrowings	550.0	620.0	0.0
Repayments	(21.0)	(690.8)	(335.6)
Common stock repurchased and retired	(50.0)
Stock options exercised	3.4	29.8	0.5
Excess tax benefits from stock-based compensation			0.4
Dividends paid	(133.6)	(133.0)	(132.1)
Debt issuance costs	(8.5)	(8.3)	0.0
Intercompany financing activities	(780.4)	(171.4)	(203.8)
Net financing activities	(440.1)	(353.7)	(670.6)
Effect of exchange rate changes on cash and cash equivalents	0.0	0.0	0.0
Net (decrease) increase in cash and cash equivalents	34.9	31.9	(94.2)
Cash and cash equivalents, beginning of year	57.1	25.2	119.4
Cash and cash equivalents, end of year	92.0	57.1	25.2
Issuer
Supplemental Guarantor Financial Information Statements Of Cash Flows [Line Items]
Net cash provided by (used for) operating activities	0.0	0.0	0.0
Capital expenditures	0.0	0.0	0.0
Business acquired and related transactions, net of cash acquired			0.0
Payments under long-term supply contracts		0.0	0.0
Proceeds from sale/leaseback of equipment			0.0
Proceeds from disposition of property, plant and equipment	0.0	0.0	0.0
Proceeds from disposition of affiliated companies			0.0
Distributions from consolidated subsidiaries, net	95.0	0.0
Net investing activities	95.0	0.0	0.0
Long-term debt:
Borrowings	0.0	1,375.0	0.0
Repayments	(780.4)	(1,334.1)	(67.5)
Common stock repurchased and retired	0.0
Stock options exercised	0.0	0.0	0.0
Excess tax benefits from stock-based compensation			0.0
Dividends paid	(95.0)	0.0	0.0
Debt issuance costs	0.0	(2.9)	(1.0)
Intercompany financing activities	780.4	(38.0)	68.5
Net financing activities	(95.0)	0.0	0.0
Effect of exchange rate changes on cash and cash equivalents	0.0	0.0	0.0
Net (decrease) increase in cash and cash equivalents	0.0	0.0	0.0
Cash and cash equivalents, beginning of year	0.0	0.0	0.0
Cash and cash equivalents, end of year	0.0	0.0	0.0
Subsidiary Non-Guarantor
Supplemental Guarantor Financial Information Statements Of Cash Flows [Line Items]
Net cash provided by (used for) operating activities	378.0	176.8	(99.4)
Capital expenditures	(235.4)	(205.2)	(212.3)
Business acquired and related transactions, net of cash acquired			0.0
Payments under long-term supply contracts		(209.4)	(175.7)
Proceeds from sale/leaseback of equipment			40.4
Proceeds from disposition of property, plant and equipment	2.9	5.2	0.3
Proceeds from disposition of affiliated companies			0.0
Distributions from consolidated subsidiaries, net	0.0	0.0
Net investing activities	(232.5)	(409.4)	(347.3)
Long-term debt:
Borrowings	20.0	40.5	230.0
Repayments	(144.7)	(13.0)	(32.2)
Common stock repurchased and retired	0.0
Stock options exercised	0.0	0.0	0.0
Excess tax benefits from stock-based compensation			0.0
Dividends paid	(95.0)	(2.7)	0.0
Debt issuance costs	0.0	0.0	0.0
Intercompany financing activities	0.0	209.4	135.3
Net financing activities	(219.7)	234.2	333.1
Effect of exchange rate changes on cash and cash equivalents	(0.3)	0.4	0.3
Net (decrease) increase in cash and cash equivalents	(74.5)	2.0	(113.3)
Cash and cash equivalents, beginning of year	161.3	159.3	272.6
Cash and cash equivalents, end of year	86.8	161.3	159.3
Eliminations
Supplemental Guarantor Financial Information Statements Of Cash Flows [Line Items]
Net cash provided by (used for) operating activities	0.0	0.0	0.0
Capital expenditures	0.0	0.0	0.0
Business acquired and related transactions, net of cash acquired			0.0
Payments under long-term supply contracts		0.0	0.0
Proceeds from sale/leaseback of equipment			0.0
Proceeds from disposition of property, plant and equipment	0.0	0.0	0.0
Proceeds from disposition of affiliated companies			0.0
Distributions from consolidated subsidiaries, net	(190.0)	(2.7)
Net investing activities	(190.0)	(2.7)	0.0
Long-term debt:
Borrowings	0.0	0.0	0.0
Repayments	0.0	0.0	0.0
Common stock repurchased and retired	0.0
Stock options exercised	0.0	0.0	0.0
Excess tax benefits from stock-based compensation			0.0
Dividends paid	190.0	2.7	0.0
Debt issuance costs	0.0	0.0	0.0
Intercompany financing activities	0.0	0.0	0.0
Net financing activities	190.0	2.7	0.0
Effect of exchange rate changes on cash and cash equivalents	0.0	0.0	0.0
Net (decrease) increase in cash and cash equivalents	0.0	0.0	0.0
Cash and cash equivalents, beginning of year	0.0	0.0	0.0
Cash and cash equivalents, end of year	$ 0.0	$ 0.0	$ 0.0