Marketable Securities - Schedule of Investments in Available For Sale Debt Securities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 4,584.1	$ 3,649.2
Unrealized Gains	29.3	40.1
Unrealized Losses	(6.2)	(0.2)
Fair Value	4,607.2	3,689.1
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	3,610.4	3,053.0
Unrealized Gains	27.7	37.5
Unrealized Losses	(5.9)	(0.2)
Fair Value	3,632.2	3,090.3
U.S. government and government agency obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	487.4	127.6
Unrealized Gains	0.6	1.3
Unrealized Losses	(0.2)	0.0
Fair Value	487.8	128.9
Sovereign bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	65.0	65.2
Unrealized Gains	0.8	1.1
Unrealized Losses	(0.1)	0.0
Fair Value	65.7	66.3
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	254.2	276.0
Unrealized Gains	0.1	0.1
Unrealized Losses	0.0	0.0
Fair Value	254.3	276.1
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	167.1	127.4
Unrealized Gains	0.1	0.1
Unrealized Losses	0.0	0.0
Fair Value	$ 167.2	$ 127.5