INCOME TAXES - Income tax expense (benefit), income tax reconciliation and components of deferred tax assets and liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income tax provision (benefit), income tax reconciliation [Abstract]
U.K. statutory rate	19.00%	19.25%	20.00%
Tax at statutory rate	$ (75.8)	$ 19.1	$ 65.1
Foreign rate differential	9.6	(39.5)	(92.7)
Deferred intercompany gain/loss	0.0	0.0	(20.1)
Foreign asset basis difference	1.8	(38.1)	405.9
Luxembourg restructuring operating loss (2)	(22.9)	0.0	(1,180.2)
Change in valuation allowance	37.6	(29.4)	814.7
Prior period adjustments	(2.9)	3.6	(4.1)
Unrecognized tax benefits	(4.7)	(24.1)	7.1
U.S. tax on RCI non-U.S. subsidiaries	9.4	5.4	6.3
Effective Income Tax Rate Reconciliation, Effect of Tax Cuts and Jobs Act of 2017	(7.4)	129.1	0.0
Foreign tax credits/deductions	0.0	(0.8)	(1.5)
Other, net	3.7	1.3	4.5
Total provision (benefit)	(51.6)	26.6	5.0
Deferred tax assets
Accrued employee benefit plan costs	48.2	46.2
U.S. net operating loss	40.6	39.3
Other NOLs and tax credit carryforwards	38.0	38.1
Other	18.6	16.3
Total deferred tax assets	1,409.9	1,315.3
Less: valuation allowance	(905.9)	(869.9)
Deferred tax assets, net of valuation allowance	504.0	445.4
Deferred tax liabilities
Property and equipment	396.2	412.8
Other	12.3	11.9
Total deferred tax liabilities	408.5	424.7
Net deferred tax asset (liability)	95.5	20.7
U.K. [Member]
Deferred tax assets
Foreign net operating loss	6.0	2.4
Trinidad [Member]
Deferred tax assets
Foreign net operating loss	5.2	5.9
Luxembourg [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards			4,534.0
Deferred tax assets
Foreign net operating loss	1,249.4	1,163.2	1,180.0
Deferred Tax Liabilities, Book Over Tax Asset Basis Difference			409.0
Less: valuation allowance	(867.9)	(766.5)	$ (747.0)
Suriname [Member]
Deferred tax assets
Foreign net operating loss	$ 3.9	$ 3.9