Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2021

Investments, Debt and Equity Securities [Abstract]

The following tables summarize the Company's investments in available-for-sale debt securities:


(In millions)	Amortized		Unrealized				Fair
As of March 31, 2021	Cost Basis		Gains		Losses		Value
Corporate bonds	$	3,610.4	$	27.7	$	(5.9)	$	3,632.2
U.S. government and government agency obligations	487.4		0.6		(0.2)		487.8
Sovereign bonds	65.0		0.8		(0.1)		65.7
Commercial paper	254.2		0.1		—		254.3
Certificates of deposit	167.1		0.1		—		167.2
	$	4,584.1	$	29.3	$	(6.2)	$	4,607.2

As of December 31, 2020
Corporate bonds	$	3,053.0	$	37.5	$	(0.2)	$	3,090.3
U.S. government and government agency obligations	127.6		1.3		—		128.9
Sovereign bonds	65.2		1.1		—		66.3
Commercial paper	276.0		0.1		—		276.1
Certificates of deposit	127.4		0.1		—		127.5
	$	3,649.2	$	40.1	$	(0.2)	$	3,689.1

Marketable Securities, Based on Contractual Maturity Dates

The fair values of available-for-sale debt securities by contractual maturity consist of the following:


	March 31,		December 31,
(In millions)	2021		2020
Maturities within one year	$	2,065.9	$	1,393.3
Maturities after one year through five years	2,541.3		2,295.8
	$	4,607.2	$	3,689.1

Fair Value and Unrealized Losses of Marketable Securities

The following table shows the fair value of the Company's available-for-sale debt securities that have unrealized losses, aggregated by investment category and length of time that the individual securities have been in a continuous loss position.


	Less than 12 Months				12 Months or Greater		Total
(In millions) As of March 31, 2021	Fair Value		Unrealized Loss		Fair Value	Unrealized Loss	Fair Value		Unrealized Loss
Corporate bonds	$	1,304.1	$	(5.9)	—	—	$	1,304.1	$	(5.9)
U.S. government and government agency obligations	123.1		(0.2)		—	—	123.1		(0.2)
Sovereign bonds	28.0		(0.1)		—	—	28.0		(0.1)
	$	1,455.2	$	(6.2)	—	—	$	1,455.2	$	(6.2)

As of December 31, 2020
Corporate bonds	$	364.5	$	(0.2)	—	—	$	364.5	$	(0.2)