Cash, Cash Equivalents, and Marketable Debt Securities (Tables)

3 Months Ended

Mar. 31, 2021

Cash Cash Equivalents And Short Term Investments [Abstract]

Schedule of Cash and Available-For-Sale Debt Securities by Major Asset Category

The following table shows the Company’s cash and available-for-sale (AFS) debt securities by major asset category at March 31, 2021 and December 31, 2020 (in millions):

	March 31, 2021
	Adjusted Cost Basis		Unrealized Gain		Unrealized Loss		Fair Value		Cash and Cash Equivalents		Short-Term Marketable Debt Securities		Long-Term Marketable Debt Securities
Cash and cash equivalents	$	980.4	$	—	$	—	$	980.4	$	980.4	$	—	$	—
Level 1 (a):
Money market funds		1.8		—		—		1.8		1.8		—		—
U.S. Treasury securities		28.9		0.1		—		29.0		—		22.5		6.5
Subtotal		30.7		0.1		—		30.8		1.8		22.5		6.5
Level 2 (b):
Certificates of deposit		7.3		—		—		7.3		1.2		6.1		—
Commercial paper		2.3		—		—		2.3		—		2.3		—
U.S. government agency securities		7.1		—		—		7.1		—		2.6		4.5
Corporate debt securities		104.8		0.2		—		105.0		—		69.0		36.0
Subtotal		121.5		0.2		—		121.7		1.2		80.0		40.5
Total	$	1,132.6	$	0.3	$	—	$	1,132.9	$	983.4	$	102.5	$	47.0

	December 31, 2020
	Adjusted Cost Basis		Unrealized Gain		Unrealized Loss		Fair Value		Cash and Cash Equivalents		Short-Term Marketable Debt Securities		Long-Term Marketable Debt Securities
Cash and cash equivalents	$	970.5	$	—	$	—	$	970.5	$	970.5	$	—	$	—
Level 1 (a):
Money market funds		0.6		—		—		0.6		0.6		—		—
U.S. Treasury securities		28.1		0.2		—		28.3		—		18.9		9.4
Subtotal		28.7		0.2		—		28.9		0.6		18.9		9.4
Level 2 (b):
Certificates of deposit		5.9		—		—		5.9		1.1		4.8		—
Commercial paper		3.2		—		—		3.2		1.0		2.2		—
U.S. government agency securities		6.6		—		—		6.6		—		2.6		4.0
Corporate debt securities		107.5		0.3		—		107.8		1.4		77.1		29.3
Subtotal		123.2		0.3		—		123.5		3.5		86.7		33.3
Total	$	1,122.4	$	0.5	$	—	$	1,122.9	$	974.6	$	105.6	$	42.7

(a) Valuations based on quoted prices for identical assets or liabilities in active markets.

(b) Valuations based on observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data.

Schedule of Marketable Debt Securities in Continuous Loss Position

The following table provides information about the Company’s marketable debt securities that have been in a continuous loss position as of March 31, 2021 and December 31, 2020 (in millions, except number of marketable debt securities in a loss position):

	March 31, 2021						December 31, 2020
	Fair Value of Marketable Debt Securities		Number of Marketable Debt Securities in a Loss Position		Unrealized Losses (c)		Fair Value of Marketable Debt Securities		Number of Marketable Debt Securities in a Loss Position		Unrealized Losses (c)
Corporate debt securities	$	60.4	79		$	—	$	42.9	56		$	—
U.S. Treasury securities		2.5	5			—		1.7	3			—
Certificates of deposit		1.2	2			—		1.3	2			—
U.S. government agency securities		0.5	1			—		—		—		—
Commercial paper		—		—		—		2.2	1			—
	$	64.6	87		$	—	$	48.1	62		$	—

(c) Unrealized losses were insignificant for the periods ended March 31, 2021 and December 31, 2020.