SUPPLEMENTAL GUARANTOR FINANCIAL INFORMATION (Statements of Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Supplemental Guarantor Financial Information Statements Of Comprehensive Income (Loss) [Line Items]
Net income	$ 44.2	$ (20.0)	$ 41.7	$ 195.1	$ 58.6	$ 20.9	$ 65.9	$ 274.6
Other comprehensive (loss) income net of tax:
Foreign currency translation adjustments, net	(15.7)			(2.0)			(20.7)	(15.7)
Unrealized losses on derivative contracts, net	(2.5)			(3.6)			(17.9)	(6.1)
Amortization of prior service costs and actuarial losses, net	5.9			7.5			16.9	21.0
Total other comprehensive (loss) income, net of tax	(12.3)	$ (3.5)	$ (5.9)	1.9	$ (20.4)	$ 17.7	(21.7)	(0.8)
Comprehensive income	31.9			197.0			44.2	273.8
Parent Guarantor
Supplemental Guarantor Financial Information Statements Of Comprehensive Income (Loss) [Line Items]
Net income	44.2			195.1			65.9	274.6
Other comprehensive (loss) income net of tax:
Foreign currency translation adjustments, net	0.0			0.0			0.0	0.0
Unrealized losses on derivative contracts, net	(2.5)			(3.6)			(17.9)	(6.1)
Amortization of prior service costs and actuarial losses, net	4.9			6.6			14.8	19.7
Total other comprehensive (loss) income, net of tax	2.4			3.0			(3.1)	13.6
Comprehensive income	46.6			198.1			62.8	288.2
Issuer
Supplemental Guarantor Financial Information Statements Of Comprehensive Income (Loss) [Line Items]
Net income	45.9			57.0			35.5	107.3
Other comprehensive (loss) income net of tax:
Foreign currency translation adjustments, net	0.0			0.0			0.0	0.0
Unrealized losses on derivative contracts, net	0.0			0.0			0.0	0.0
Amortization of prior service costs and actuarial losses, net	0.0			0.0			0.0	0.0
Total other comprehensive (loss) income, net of tax	0.0			0.0			0.0	0.0
Comprehensive income	45.9			57.0			35.5	107.3
Subsidiary Non-Guarantor
Supplemental Guarantor Financial Information Statements Of Comprehensive Income (Loss) [Line Items]
Net income	105.6			150.4			233.5	337.3
Other comprehensive (loss) income net of tax:
Foreign currency translation adjustments, net	(15.7)			(2.0)			(20.7)	(15.7)
Unrealized losses on derivative contracts, net	0.0			0.0			0.0	0.0
Amortization of prior service costs and actuarial losses, net	1.0			0.9			2.1	1.3
Total other comprehensive (loss) income, net of tax	(14.7)			(1.1)			(18.6)	(14.4)
Comprehensive income	90.9			149.3			214.9	322.9
Eliminations
Supplemental Guarantor Financial Information Statements Of Comprehensive Income (Loss) [Line Items]
Net income	(151.5)			(207.4)			(269.0)	(444.6)
Other comprehensive (loss) income net of tax:
Foreign currency translation adjustments, net	0.0			0.0			0.0	0.0
Unrealized losses on derivative contracts, net	0.0			0.0			0.0	0.0
Amortization of prior service costs and actuarial losses, net	0.0			0.0			0.0	0.0
Total other comprehensive (loss) income, net of tax	0.0			0.0			0.0	0.0
Comprehensive income	$ (151.5)			$ (207.4)			$ (269.0)	$ (444.6)