Debt Securities (Tables)

3 Months Ended

Mar. 31, 2020

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 loss, allowance for credit losses, and fair value of debt securities available-for-sale at March 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	$	129.7	$	0.1	$	(0.1	)	$	—	$	129.7
Corporate debt securities	Within 1 year		323.3		0.3		(0.9	)		—		322.7
Securities of government-sponsored entities	Within 1 year		131.1		1.2		—			—		132.3
blank		$	584.1	$	1.6	$	(1.0	)	$	—	$	584.7
blank
Corporate debt securities	1 to 2 years	$	213.3	$	0.2	$	(2.2	)	$	—	$	211.3
Securities of government-sponsored entities	1 to 2 years		24.5		0.1		—			—		24.6
		$	237.8	$	0.3	$	(2.2	)	$	—	$	235.9

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
blank		$	557.3	$	0.9	$	—		$	558.2
blank
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

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 March 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
Commercial paper	$	19.9	$	(0.1	)	$	—	$	—	$	19.9	$	(0.1	)
Corporate debt securities		409.8		(3.1	)		—		—		409.8		(3.1	)
blank	$	429.7	$	(3.2	)	$	—	$	—	$	429.7	$	(3.2	)

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	)