Income Taxes - Schedule of deferred tax assets and liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Capitalized research and development expenses	$ 1,728.2	$ 845.3
Deferred compensation	413.6	416.2
Accrued expenses	214.1	235.6
Fixed assets and intangible assets	154.8	227.6
Tax attribute carryforwards	88.7	41.3
Other	26.4	15.9
Total deferred tax assets	2,625.8	1,781.9
Deferred tax liabilities:
Unrealized gains on investments	(50.4)	(58.2)
Net deferred tax assets	$ 2,575.4	$ 1,723.7