Debt Securities (Tables)

6 Months Ended

Jun. 30, 2021

Investments, Debt and Equity Securities [Abstract]

Amortized Cost, Gross Unrealized Gains and Losses, Allowance for Credit Losses and Fair Value of Debt Securities Available-For-Sale

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 June 30, 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	$	168.6	$	—	$	—	$	—	$	168.6
Corporate debt securities	Within 1 year	212.0		0.5		—		—		212.5
Securities of government-sponsored entities	Within 1 year	135.7		0.1		—		—		135.8
		$	516.3	$	0.6	$	—	$	—	$	516.9
Corporate debt securities	1 to 2 years	$	230.3	$	0.1	$	(0.2)	$	—	$	230.2
Securities of government-sponsored entities	1 to 2 years	107.6		0.1		(0.1)		—		107.6
		$	337.9	$	0.2	$	(0.3)	$	—	$	337.8

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

Gross Unrealized Losses and Fair Value Available-For-Sale Investments in Unrealized Loss Position

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 June 30, 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
June 30, 2021:
Corporate Debt Securities	$	211.0	$	(0.2)	$	—	$	—	$	211.0	$	(0.2)
Securities of government-sponsored entities	34.5		(0.1)		—		—		34.5		(0.1)
	$	245.5	$	(0.3)	$	—	$	—	$	245.5	$	(0.3)
December 31, 2020:
Securities of government-sponsored entities	$	95.0	$	(0.1)	$	—	$	—	$	95.0	$	(0.1)