INVESTMENTS - Schedule of Investments in Debt Securities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Available-for-sale
Cost	$ 825.7	$ 790.5
Gross Unrealized Gains	11.4	3.5
Gross Unrealized Losses	(0.1)	(0.2)
Fair Value	837.0	793.8
Bank time deposits
Available-for-sale
Cost	33.3	13.1
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	33.3	13.1
Held-to-maturity
Cost	0.0	100.2
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	0.0	100.2
Commercial paper
Available-for-sale
Cost	60.1	34.3
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	60.1	34.3
U.S. government and agency securities
Available-for-sale
Cost	130.3	113.2
Gross Unrealized Gains	2.5	0.6
Gross Unrealized Losses	0.0	0.0
Fair Value	132.8	113.8
Foreign government bonds
Available-for-sale
Cost	1.7	1.7
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	1.7	1.7
Asset-backed securities
Available-for-sale
Cost	135.3	141.2
Gross Unrealized Gains	1.9	0.6
Gross Unrealized Losses	0.0	(0.1)
Fair Value	137.2	141.7
Corporate debt securities
Available-for-sale
Cost	465.0	487.0
Gross Unrealized Gains	7.0	2.3
Gross Unrealized Losses	(0.1)	(0.1)
Fair Value	$ 471.9	$ 489.2

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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