Income Taxes - Schedule of deferred tax assets and liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Deferred tax assets:
Capitalized research and development expenses	$ 3,146.2	$ 2,530.2
Deferred compensation	452.0	419.7
Accrued expenses	158.8	185.0
Fixed assets and intangible assets	192.6	145.1
Tax attribute carryforwards	79.6	84.1
Other	49.9	43.0
Total deferred tax assets	4,079.1	3,407.1
Deferred tax liabilities:
Unrealized gains on investments	(1.9)	(93.0)
Net deferred tax assets	$ 4,077.2	$ 3,314.1