FINANCIAL INSTRUMENTS - Summary of Cash and Available-For-Sale Securities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	$ 1,223.8	$ 1,167.6
Total	4,625.6
Total assets measured at fair value, Amortized Cost	5,849.4	5,818.1
Gross Unrealized Gains	55.6	27.9
Gross Unrealized Losses	(7.6)	(0.8)
Allowance for Credit Loss	1.3
Total assets measured at fair value, Fair Value	5,896.1	5,845.2
Short- term Investments	2,029.6	2,054.1
Long- term Investments	2,642.7	2,623.5
Cash
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	450.3	413.1
Fair Value	450.3	413.1
Level 1
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	773.5	726.8
Total	2,664.5	2,662.6
Gross Unrealized Gains	39.9	9.7
Gross Unrealized Losses	0.0	(0.4)
Allowance for Credit Loss	0.0
Fair Value	2,704.4	2,671.9
Short- term Investments	832.7	890.8
Long- term Investments	1,098.2	1,054.3
Level 1 | Money market funds
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	773.5	726.8
Fair Value	773.5	726.8
Short- term Investments	0.0	0.0
Long- term Investments	0.0	0.0
Level 1 | U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	0.0	0.0
Total	1,891.0	1,935.8
Gross Unrealized Gains	39.9	9.7
Gross Unrealized Losses	0.0	(0.4)
Allowance for Credit Loss	0.0
Fair Value	1,930.9	1,945.1
Short- term Investments	832.7	890.8
Long- term Investments	1,098.2	1,054.3
Level 2
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	0.0	27.7
Total	2,734.6	2,742.4
Gross Unrealized Gains	15.7	18.2
Gross Unrealized Losses	(7.6)	(0.4)
Allowance for Credit Loss	1.3
Fair Value	2,741.4	2,760.2
Short- term Investments	1,196.9	1,163.3
Long- term Investments	1,544.5	1,569.2
Level 2 | Commercial paper
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	0.0	25.5
Total	148.7	165.1
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Allowance for Credit Loss	0.0
Fair Value	148.7	165.1
Short- term Investments	148.7	139.6
Long- term Investments	0.0	0.0
Level 2 | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	0.0	0.0
Total	2,086.0	2,096.1
Gross Unrealized Gains	11.1	16.8
Gross Unrealized Losses	(7.5)	(0.2)
Allowance for Credit Loss	1.3
Fair Value	2,088.3	2,112.7
Short- term Investments	839.4	798.5
Long- term Investments	1,248.9	1,314.2
Level 2 | U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	0.0	0.0
Total	414.5	418.3
Gross Unrealized Gains	4.0	1.1
Gross Unrealized Losses	0.0	(0.2)
Allowance for Credit Loss	0.0
Fair Value	418.5	419.2
Short- term Investments	185.9	209.6
Long- term Investments	232.6	209.6
Level 2 | Non-U.S. government securities
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	0.0	0.0
Total	4.5	4.5
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Allowance for Credit Loss	0.0
Fair Value	4.5	4.5
Short- term Investments	4.5	4.5
Long- term Investments	0.0	0.0
Level 2 | Municipal securities
Debt Securities, Available-for-sale [Line Items]
Cash and cash equivalents	0.0	2.2
Total	80.9	58.4
Gross Unrealized Gains	0.6	0.3
Gross Unrealized Losses	(0.1)	0.0
Allowance for Credit Loss	0.0
Fair Value	81.4	58.7
Short- term Investments	18.4	11.1
Long- term Investments	$ 63.0	$ 45.4