Debt Securities

6 Months Ended

Jun. 30, 2024

Investments, Debt and Equity Securities [Abstract]

The following table presents the amortized cost, unrealized gain and loss recognized in accumulated other comprehensive income (loss) and fair value of debt securities available-for-sale, aggregated by major security type and contractual maturity.


		June 30, 2024								December 31, 2023
(in millions)	Contractual Maturity	Amortized Cost		Unrealized Gain		Unrealized Loss		Fair Value		Amortized Cost		Unrealized Gain		Unrealized Loss		Fair Value
Commercial paper	0 to 1 years	$	57.2	$	—	$	—	$	57.2	$	53.5	$	—	$	—	$	53.5
Corporate debt securities	0 to 1 years	530.9		0.1		(1.2)		529.8		382.1		0.1		(1.0)		381.2
Securities of government-sponsored entities	0 to 1 years	312.7		—		(0.5)		312.2		346.1		0.2		(0.5)		345.8
		$	900.8	$	0.1	$	(1.7)	$	899.2	$	781.7	$	0.3	$	(1.5)	$	780.5

Corporate debt securities	1 to 3 years	$	476.4	$	0.4	$	(1.7)	$	475.1	$	483.5	$	2.9	$	(0.4)	$	486.0
Securities of government-sponsored entities	1 to 3 years	163.4		—		(0.7)		162.7		201.1		0.5		(0.1)		201.5
		$	639.8	$	0.4	$	(2.4)	$	637.8	$	684.6	$	3.4	$	(0.5)	$	687.5

Unrealized losses on our available-for-sale debt security investments were primarily due to changes in interest rates. These investments are of high credit quality, and 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. No allowance for credit losses was recognized as of June 30, 2024 or December 31, 2023.

The following table presents debt securities available-for-sale that were in an unrealized loss position as of June 30, 2024, aggregated by major security type and length of time in a continuous 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	$	678.2	$	(2.3)	$	104.0	$	(0.6)	$	782.2	$	(2.9)
Securities of government-sponsored entities	$	386.7	$	(1.0)	$	51.0	$	(0.2)	$	437.7	$	(1.2)

The following table presents debt securities available-for-sale that were in an unrealized loss position as of December 31, 2023, aggregated by major security type and length of time in a continuous 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	$	265.1	$	(0.4)	$	183.8	$	(1.0)	$	448.9	$	(1.4)
Securities of government-sponsored entities	$	214.6	$	(0.2)	$	16.7	$	(0.4)	$	231.3	$	(0.6)

Accrued interest receivables on debt securities available-for-sale totaled $12.6 million and $11.2 million, respectively, as of June 30, 2024 and December 31, 2023. 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 first six months of 2024 or 2023.