SUPPLEMENTAL GUARANTOR FINANCIAL INFORMATION (Statements of Comprehensive Income)(Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Guarantor Financial Information Statements Of Comprehensive Income [Line Items]
Net income (loss)	$ 53.3	$ 195.1	$ 58.6	$ 20.9	$ 489.3	$ 52.7	$ (5.9)	$ 13.4	$ 327.9	$ 549.5	$ (3.9)
Foreign currency translation adjustments, net									(22.2)	31.7	(12.0)
Unrealized (losses) gains on derivative contracts, net									(11.7)	(1.7)	19.7
Pension and postretirement liability adjustments, net									(74.9)	(21.6)	(37.5)
Amortization of prior service costs and actuarial losses, net									28.3	17.0	12.3
Total other comprehensive (loss) income, net of tax									(80.5)	25.4	(17.5)
Comprehensive income (loss)									247.4	574.9	(21.4)
Parent Guarantor
Supplemental Guarantor Financial Information Statements Of Comprehensive Income [Line Items]
Net income (loss)									327.9	549.5	(3.9)
Foreign currency translation adjustments, net									0.0	0.0	0.0
Unrealized (losses) gains on derivative contracts, net									(11.7)	(1.7)	19.7
Pension and postretirement liability adjustments, net									(69.6)	(12.3)	(25.3)
Amortization of prior service costs and actuarial losses, net									26.3	15.3	10.9
Total other comprehensive (loss) income, net of tax									(55.0)	1.3	5.3
Comprehensive income (loss)									272.9	550.8	1.4
Issuer
Supplemental Guarantor Financial Information Statements Of Comprehensive Income [Line Items]
Net income (loss)									171.4	501.8	42.7
Foreign currency translation adjustments, net									0.0	0.0	0.0
Unrealized (losses) gains on derivative contracts, net									0.0	0.0	0.0
Pension and postretirement liability adjustments, net									0.0	0.0	0.0
Amortization of prior service costs and actuarial losses, net									0.0	0.0	0.0
Total other comprehensive (loss) income, net of tax									0.0	0.0	0.0
Comprehensive income (loss)									171.4	501.8	42.7
Subsidiary Non-Guarantor
Supplemental Guarantor Financial Information Statements Of Comprehensive Income [Line Items]
Net income (loss)									428.9	494.2	112.5
Foreign currency translation adjustments, net									(22.2)	31.7	(12.0)
Unrealized (losses) gains on derivative contracts, net									0.0	0.0	0.0
Pension and postretirement liability adjustments, net									(5.3)	(9.3)	(12.2)
Amortization of prior service costs and actuarial losses, net									2.0	1.7	1.4
Total other comprehensive (loss) income, net of tax									(25.5)	24.1	(22.8)
Comprehensive income (loss)									403.4	518.3	89.7
Eliminations
Supplemental Guarantor Financial Information Statements Of Comprehensive Income [Line Items]
Net income (loss)									(600.3)	(996.0)	(155.2)
Foreign currency translation adjustments, net									0.0	0.0	0.0
Unrealized (losses) gains on derivative contracts, net									0.0	0.0	0.0
Pension and postretirement liability adjustments, net									0.0	0.0	0.0
Amortization of prior service costs and actuarial losses, net									0.0	0.0	0.0
Total other comprehensive (loss) income, net of tax									0.0	0.0	0.0
Comprehensive income (loss)									$ (600.3)	$ (996.0)	$ (155.2)