Marketable Securities - Schedule of Investments in Available For Sale Debt Securities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 2,890.3	$ 4,206.3
Unrealized Gains	44.9	28.5
Unrealized Losses	(0.7)	(0.3)
Fair Value	2,934.5	4,234.5
Corporate bonds \| Unrestricted
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	2,393.2	3,960.5
Unrealized Gains	41.9	27.8
Unrealized Losses	(0.7)	(0.2)
Fair Value	2,434.4	3,988.1
U.S. government and government agency obligations \| Unrestricted
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	81.6	54.3
Unrealized Gains	1.1	0.2
Unrealized Losses	0.0	(0.1)
Fair Value	82.7	54.4
Sovereign bonds \| Unrestricted
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	27.0	26.9
Unrealized Gains	1.2	0.4
Unrealized Losses	0.0	0.0
Fair Value	28.2	27.3
Commercial paper \| Unrestricted
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	283.1	92.3
Unrealized Gains	0.6	0.0
Unrealized Losses	0.0	0.0
Fair Value	283.7	92.3
Certificates of deposit \| Unrestricted
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	105.4	72.3
Unrealized Gains	0.1	0.1
Unrealized Losses	0.0	0.0
Fair Value	$ 105.5	$ 72.4

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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