Segment Information - Schedule of Significant Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Segment Reporting Information [Line Items]
Research and development	$ 1,475.0	$ 1,271.5	$ 4,224.1	$ 3,719.9
Reportable Segment
Segment Reporting Information [Line Items]
Research and development	1,475.0	1,271.5	4,224.1	3,719.9
Reimbursement of research and development expenses by collaborators	(32.8)	(51.0)	(112.5)	(139.4)
Reportable Segment | Clinical manufacturing costs
Segment Reporting Information [Line Items]
Research and development	381.4	306.6	1,028.8	841.3
Reportable Segment | Direct research and development expenses
Segment Reporting Information [Line Items]
Research and development	454.3	386.4	1,296.7	1,158.5
Reportable Segment | Indirect research and development expenses:
Segment Reporting Information [Line Items]
Research and development	672.1	629.5	2,011.1	1,859.5
Reportable Segment | Indirect research and development expenses: | Payroll and benefits
Segment Reporting Information [Line Items]
Research and development	438.3	407.8	1,339.5	1,249.2
Reportable Segment | Indirect research and development expenses: | Lab supplies and other research and development costs
Segment Reporting Information [Line Items]
Research and development	67.5	63.0	192.4	175.4
Reportable Segment | Indirect research and development expenses: | Occupancy and other operating costs
Segment Reporting Information [Line Items]
Research and development	$ 166.3	$ 158.7	$ 479.2	$ 434.9