Debt Securities (Tables)

6 Months Ended

Jun. 30, 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 June 30, 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			$	140.0	$	0.1	$	—	—		$	140.1
Corporate debt securities	Within 1 year			287.8		2.0		—		—		289.8
Securities of government-sponsored entities	Within 1 year			102.5		0.8		—		—		103.3
				$	530.3	$	2.9	$	—	$	—	$	533.2
Corporate debt securities	1	to	2 years	$	173.5	$	1.7	$	—	—		$	175.2
Securities of government-sponsored entities	1	to	2 years	20.0		—		—		—		20.0
				$	193.5	$	1.7	$	—	$	—	$	195.2

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

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 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)