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Financial Instruments - Summary of Marketable Securities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 2,049.1	$ 2,965.0
Gross Unrealized Gains	2.3	6.0
Gross Unrealized Losses	(0.4)	(0.7)
Fair Value	2,051.0	2,970.3
Corporate debt securities Current
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	897.8	1,057.2
Gross Unrealized Gains	0.4	1.0
Gross Unrealized Losses	(0.2)	0.0
Fair Value	898.0	1,058.2
Corporate debt securities Non-current
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	402.5	633.9
Gross Unrealized Gains	1.1	3.0
Gross Unrealized Losses	(0.1)	0.0
Fair Value	403.5	636.9
Government securities Current
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	380.6	502.9
Gross Unrealized Gains	0.1	0.4
Gross Unrealized Losses	0.0	0.0
Fair Value	380.7	503.3
Government securities Non-current
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	245.9	510.1
Gross Unrealized Gains	0.5	0.8
Gross Unrealized Losses	0.0	(0.3)
Fair Value	246.4	510.6
Mortgage and other asset backed securities Current
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0.2	0.7
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Fair Value	0.2	0.7
Mortgage and other asset backed securities Non-current
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	122.1	260.2
Gross Unrealized Gains	0.2	0.8
Gross Unrealized Losses	(0.1)	(0.4)
Fair Value	122.2	260.6
Marketable equity securities, current
Debt Securities, Available-for-sale [Line Items]
Marketable equity securities, amortized cost	70.6
Marketable equity securities, gross unrealized gains	15.9
Marketable equity securities, gross unrealized losses	0.0
Marketable equity securities, fair value	86.5
Marketable equity securities, non-current
Debt Securities, Available-for-sale [Line Items]
Marketable equity securities, amortized cost	1,168.9	218.4
Marketable equity securities, gross unrealized gains	733.8	132.1
Marketable equity securities, gross unrealized losses	(14.9)	(13.0)
Marketable equity securities, fair value	$ 1,887.8	$ 337.5

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