Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2025

Fair Value Disclosures [Abstract]

Schedule of Fair Value of Financial Assets by Level

The following tables summarize the fair value of these financial assets by significant investment category and their levels within the fair value hierarchy (in millions):

	March 31, 2025								December 31, 2024
	Level I		Level II		Level III		Total		Level I		Level II		Level III		Total
Financial Assets:
Cash Equivalents:
Money market funds	$	782.7	$	—	$	—	$	782.7	$	1,707.5	$	—	$	—	$	1,707.5
Commercial paper	—		62.1		—		62.1		—		—		—		—
U.S. government notes	288.9		—		—		288.9		31.4		—		—		31.4
Agency securities	—		—		—		—		—		3.0		—		3.0
	1,071.6		62.1		—		1,133.7		1,738.9		3.0		—		1,741.9
Marketable Securities:
Commercial paper	—		43.3		—		43.3		—		48.8		—		48.8
U.S. government notes	2,094.8		—		—		2,094.8		1,921.5		—		—		1,921.5
Corporate bonds	—		3,111.8		—		3,111.8		—		2,593.6		—		2,593.6
Agency securities	—		1,054.6		—		1,054.6		—		977.2		—		977.2
	2,094.8		4,209.7		—		6,304.5		1,921.5		3,619.6		—		5,541.1
Other Assets:
Money market funds - restricted	1.4		—		—		1.4		1.4		—		—		1.4
Total Financial Assets	$	3,167.8	$	4,271.8	$	—	$	7,439.6	$	3,661.8	$	3,622.6	$	—	$	7,284.4

The following table summarizes the amortized cost, unrealized gains and losses, and fair value of our debt securities measured at fair value on a recurring basis (in millions):

	March 31, 2025								December 31, 2024
	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value		Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Commercial paper	$	105.4	$	—	$	—	$	105.4	$	48.8	$	—	$	—	$	48.8
U.S. government	2,380.1		5.2		(1.6)		2,383.7		1,954.8		2.7		(4.6)		1,952.9
Corporate bonds	3,107.2		7.3		(2.7)		3,111.8		2,595.7		4.4		(6.5)		2,593.5
Agency securities	1,053.7		1.8		(0.9)		1,054.6		981.0		1.6		(2.4)		980.3
Total	$	6,646.4	$	14.3	$	(5.2)	$	6,655.5	$	5,580.3	$	8.7	$	(13.5)	$	5,575.5

Schedule of Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value

The following table is an analysis of our debt securities in unrealized loss positions (in millions):

	March 31, 2025
	Unrealized Losses within 12 months				Unrealized Losses 12 months or greater				Total
	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
U.S. government notes	$	859.3	$	(1.6)	$	—	$	—	$	859.3	$	(1.6)
Corporate bonds	896.6		(2.7)		2.8		—		899.4		(2.7)
Agency securities	483.5		(0.9)		—		—		483.5		(0.9)
Total	$	2,239.4	$	(5.2)	$	2.8	$	—	$	2,242.2	$	(5.2)

Schedule of Fair Value of Available-for-Sale Investments by Contractual Maturity

The fair values of marketable debt securities, by remaining contractual maturities, are as follows (in millions):

	March 31, 2025
	Fair Value
Due in 1 year or less	$	2,534.6
Due in 1 to 3 years	3,769.9
Total debt securities	$	6,304.5