INCOME TAXES - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Tax Credit Carryforwards
Excess tax benefit attributable to stock-based compensation		$ 143.3	$ 361.8
Excess tax benefit attributable to stock-based compensation that reduces income taxes payable		142.2
Excess tax benefit attributable to stock-based compensation that increases deferred tax asset		1.1
Excess tax benefits from stock-based awards				$ 51.8
Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]
Income tax benefit related to net operating loss carryforwards		9.5
Tax credit carryforwards		105.4
Tax credit carryforwards that can be carried forward indefinitely		24.2
Tax credit carryforwards expiring primarily by 2018 and 2037		81.2
Valuation Allowance
Decrease in valuation allowance		16.7
Valuation allowance at end of period		115.9
Income Taxes Paid, Net [Abstract]
Interest on income taxes accrued		3.4	3.0
Income tax penalties accrued		1.4	1.7
Unrecognized tax benefits including tax interest accrued		52.3	39.7
Tax positions for which the ultimate deductibility is highly certain but timing is uncertain		49.1	37.2
Change in unrecognized tax benefits unrelated to Federal income taxes statute of limitations expiring within twelve months of current reporting period		21.6
Tax benefits that would impact effective tax rate		21.6
Reduction in the Transition Tax	$ 9.2
Tax on earnings of foreign subsidiaries		1.0
Earnings of foreign subsidiaries		103.1
Federal Tax Authority
Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]
Net operating loss carryforwards		856.0
Net operating loss carryforwards not subject to expiration		13.9
Net operating loss carryforwards without restrictions		569.9
State Tax Authority
Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]
Net operating loss carryforwards		698.7
Net operating loss carryforwards without restrictions		350.4
Tax credit carryforwards		3.9
Foreign Tax Authority
Deferred Tax Assets, Operating Loss Carryforwards, Components [Abstract]
Net operating loss carryforwards		383.4
Net operating loss carryforwards not subject to expiration		352.0
Net operating loss carryforwards subject to expiration within 20 years		31.4
Tax credit carryforwards		53.2
Tax credit carryforwards related to research and development		48.3
Continuing Operations
Income Taxes Paid, Net [Abstract]
Unrecognized tax (benefit) expense net of related deferred taxes		0.3	(0.1)	0.4
Deferred taxes for interest on unrecognized tax benefits (continuing operations)		$ 0.1	$ 0.1	$ 0.2