Debt Securities

3 Months Ended

Mar. 31, 2021

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 March 31, 2021, 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	$	93.2	$	—	$	—	$	—	$	93.2
Corporate debt securities	Within 1 year	239.6		0.9		—		—		240.5
Securities of government-sponsored entities	Within 1 year	187.4		—		—		—		187.4
		$	520.2	$	0.9	$	—	$	—	$	521.1

Corporate debt securities	1 to 2 years	$	169.0	$	0.1	$	(0.2)	$	—	$	168.9
Securities of government-sponsored entities	1 to 2 years	80.6		0.1		—		—		80.7
		$	249.6	$	0.2	$	(0.2)	$	—	$	249.6

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 debt securities available-for-sale in an unrealized loss position for which an allowance for credit losses has not been recorded at March 31, 2021 and 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
March 31, 2021:
Corporate Debt Securities	$	164.6	$	(0.2)	$	—	$	—	$	164.6	$	(0.2)
December 31, 2020:
Securities of government-sponsored entities	$	95.0	$	(0.1)	$	—	$	—	$	95.0	$	(0.1)

At March 31, 2021, our security portfolio consisted of 126 securities related to investments in debt securities available-for-sale, of which 39 securities were in an unrealized loss position.

Our investments in corporate debt securities in an unrealized loss position at March 31, 2021 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.

Accrued interest receivables on debt securities available-for-sale totaled $3.2 million and $3.7 million at March 31, 2021 and December 31, 2020, respectively. We do not measure an allowance for credit losses for accrued interest receivables. For the purposes of identifying and measuring an impairment, accrued interest is excluded from both the fair value and amortized cost basis of the debt security. Uncollectible accrued interest receivables associated with an impaired debt security are reversed against interest income upon identification of the impairment. No accrued interest receivables were written off during the three months ended March 31, 2021 or 2020.