SUPPLEMENTAL GUARANTOR FINANCIAL INFORMATION (Statements of Comprehensive Income)(Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Guarantor Financial Information Statements Of Comprehensive Income [Line Items]
Net income (loss)	$ 489.3	$ 52.7	$ (5.9)	$ 13.4	$ 17.5	$ 17.5	$ (1.0)	$ (37.9)	$ 549.5	$ (3.9)	$ (1.4)
Foreign currency translation adjustments, net									31.7	(12.0)	(9.8)
Unrealized (losses) gains on derivative contracts, net									(1.7)	19.7	(2.7)
Pension and postretirement liability adjustments, net									(21.6)	(37.5)	(78.8)
Amortization of prior service costs and actuarial losses, net									17.0	12.3	41.9
Total other comprehensive income (loss), net of tax									25.4	(17.5)	(49.4)
Comprehensive income (loss)									574.9	(21.4)	(50.8)
Parent Guarantor
Supplemental Guarantor Financial Information Statements Of Comprehensive Income [Line Items]
Net income (loss)									549.5	(3.9)	(1.4)
Foreign currency translation adjustments, net									0.0	0.0	0.0
Unrealized (losses) gains on derivative contracts, net									(1.7)	19.7	(2.7)
Pension and postretirement liability adjustments, net									(12.3)	(25.3)	(73.7)
Amortization of prior service costs and actuarial losses, net									15.3	10.9	39.6
Total other comprehensive income (loss), net of tax									1.3	5.3	(36.8)
Comprehensive income (loss)									550.8	1.4	(38.2)
Issuer
Supplemental Guarantor Financial Information Statements Of Comprehensive Income [Line Items]
Net income (loss)									501.8	42.7	(4.6)
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 income (loss), net of tax									0.0	0.0	0.0
Comprehensive income (loss)									501.8	42.7	(4.6)
Subsidiary Non-Guarantor
Supplemental Guarantor Financial Information Statements Of Comprehensive Income [Line Items]
Net income (loss)									494.2	112.5	114.5
Foreign currency translation adjustments, net									31.7	(12.0)	(9.8)
Unrealized (losses) gains on derivative contracts, net									0.0	0.0	0.0
Pension and postretirement liability adjustments, net									(9.3)	(12.2)	(5.1)
Amortization of prior service costs and actuarial losses, net									1.7	1.4	2.3
Total other comprehensive income (loss), net of tax									24.1	(22.8)	(12.6)
Comprehensive income (loss)									518.3	89.7	101.9
Eliminations
Supplemental Guarantor Financial Information Statements Of Comprehensive Income [Line Items]
Net income (loss)									(996.0)	(155.2)	(109.9)
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 income (loss), net of tax									0.0	0.0	0.0
Comprehensive income (loss)									$ (996.0)	$ (155.2)	$ (109.9)