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Marketable Securities and Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Sep. 30, 2021
Fair Value, Nonrecurring \| Pfizer, Inc. \| Stock Purchase Agreement
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Non-recurring fair value measurements			$ 264.6
Level 2 \| Fair Value, Recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 1,143.2	$ 1,398.9
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(19.2)	(4.6)
Fair Value	1,124.0	1,394.3
Level 2 \| Fair Value, Recurring \| Corporate Bonds Maturing 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	802.7
Gross Unrealized Gains	0.0
Gross Unrealized Losses	(9.3)
Fair Value	793.4
Level 2 \| Fair Value, Recurring \| Corporate Bonds Maturing 2024-2025
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	205.3
Gross Unrealized Gains	0.0
Gross Unrealized Losses	(9.2)
Fair Value	196.1
Level 2 \| Fair Value, Recurring \| Government Securities Maturing 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	61.9
Gross Unrealized Gains	0.0
Gross Unrealized Losses	(0.4)
Fair Value	61.5
Level 2 \| Fair Value, Recurring \| Government Securities Maturing 2024
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	73.3
Gross Unrealized Gains	0.0
Gross Unrealized Losses	(0.3)
Fair Value	$ 73.0
Level 2 \| Fair Value, Recurring \| Corporate Bonds Maturing 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost		784.0
Gross Unrealized Gains		0.0
Gross Unrealized Losses		(0.7)
Fair Value		783.3
Level 2 \| Fair Value, Recurring \| Corporate Bonds Maturing 2023 -2024
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost		582.5
Gross Unrealized Gains		0.0
Gross Unrealized Losses		(3.8)
Fair Value		578.7
Level 2 \| Fair Value, Recurring \| Government Securities Maturing 2022
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost		32.4
Gross Unrealized Gains		0.0
Gross Unrealized Losses		(0.1)
Fair Value		$ 32.3