Debt Securities

12 Months Ended

Dec. 31, 2020

Investments, Debt and Equity Securities [Abstract]

The following table summarizes the amortized cost, unrealized gain and loss recognized in accumulated other comprehensive income (loss), allowance for credit losses, and fair value of debt securities available-for-sale at December 31, 2020, aggregated by major security type and contractual maturity:


(in millions)	Contractual Maturity	Amortized Cost		Unrealized Gain		Unrealized Loss		Allowance for Credit Losses		Fair Value
Commercial paper	Within 1 year	$	82.2	$	—	$	—	$	—	$	82.2
Corporate debt securities	Within 1 year	299.3		1.4		—		—		300.7
Securities of government-sponsored entities	Within 1 year	230.9		0.1		—		—		231.0
		$	612.4	$	1.5	$	—	$	—	$	613.9

Corporate debt securities	1 to 2 years	$	144.8	$	0.4	$	—	$	—	$	145.2
Securities of government-sponsored entities	1 to 2 years	81.9		0.1		(0.1)		—		81.9
		$	226.7	$	0.5	$	(0.1)	$	—	$	227.1

The following table summarizes the amortized cost, unrealized gain and loss recognized in accumulated other comprehensive income, and fair value of debt securities available-for-sale at December 31, 2019, aggregated by major security type and contractual maturity:


(in millions)	Contractual Maturity	Amortized Cost		Unrealized Gain		Unrealized Loss		Fair Value
Commercial paper	Within 1 year	$	144.5	$	—	$	—	$	144.5
Corporate debt securities	Within 1 year	270.5		0.5		—		271.0
Securities of government-sponsored entities	Within 1 year	142.3		0.4		—		142.7
		$	557.3	$	0.9	$	—	$	558.2

Corporate debt securities	1 to 2 years	$	250.5	$	0.5	$	(0.1)	$	250.9
Securities of government-sponsored entities	1 to 2 years	48.8		—		—		48.8
		$	299.3	$	0.5	$	(0.1)	$	299.7

The following table summarizes debt securities available-for-sale in an unrealized loss position for which an allowance for credit losses has not been recorded at December 31, 2020, aggregated by major security type and length of time in a continuous unrealized loss position:


	Less Than 12 Months				12 Months or Longer				Total
(in millions)	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Securities of government-sponsored entities	$	95.0	$	(0.1)	$	—	$	—	$	95.0	$	(0.1)

At December 31, 2020, our security portfolio consisted of 148 securities related to investments in debt securities available-for-sale, of which 30 securities were in an unrealized loss position.

Our investments in corporate debt securities in an unrealized loss position at December 31, 2020 are of high credit quality (rated A or higher). Unrealized losses on these investments were primarily due to changes in interest rates. We do not intend to sell these investments and it is not more likely than not that we will be required to sell these investments before recovery of their amortized cost basis.

The following table summarizes debt securities available-for-sale in an unrealized loss position at December 31, 2019, aggregated by major security type and length of time in a continuous unrealized loss position:


	Less Than 12 Months				12 Months or Longer				Total
(in millions)	Fair Value		Unrealized Loss		Fair Value		Unrealized Loss		Fair Value		Unrealized Loss
Corporate debt securities	$	186.1	$	(0.1)	$	—	$	—	$	186.1	$	(0.1)