Investments (Tables)

9 Months Ended

Sep. 30, 2013

Investments Debt And Equity Securities [Abstract]

Investments in Short and Long-Term Classified as Available-for-Sale Securities

We invest in short and long-term investments classified as available-for-sale securities. Information regarding our investments is as follows (in millions):

	Amortized Cost		Gross Unrealized					Fair value
			Gains		Losses
As of September 30, 2013
Corporate debt securities	$	443.5	$	0.3	$	(0.3	)	$	443.5
U.S. government and agency debt securities		252.9		0.2		—			253.1
Foreign government debt securities		3.1		—		—			3.1
Commercial paper		89.0		—		—			89.0
Certificates of deposit		67.3		—		—			67.3
Total short and long-term investments	$	855.8	$	0.5	$	(0.3	)	$	856.0
As of December 31, 2012
Corporate debt securities	$	383.6	$	0.3	$	(0.1	)	$	383.8
U.S. government and agency debt securities		295.8		0.1		—			295.9
Foreign government debt securities		5.0		—		—			5.0
Commercial paper		138.7		—		—			138.7
Certificates of deposit		92.2		0.1		—			92.3
Total short and long-term investments	$	915.3	$	0.5	$	(0.1	)	$	915.7

Fair Values and Gross Unrealized Losses for All Available-for-Sale Securities in Unrealized Loss Position Deemed to be Temporary

The following table shows the fair value and gross unrealized losses for the securities in an unrealized loss position deemed to be temporary (in millions):

	September 30, 2013					December 31, 2012
	Fair Value		Unrealized Losses			Fair value		Unrealized Losses
Corporate debt securities	$	197.4	$	(0.3	)	$	144.2	$	(0.1	)

Cost and Fair Value of Available-for-Sale Fixed-Maturity Securities by Contractual Maturity

The amortized cost and fair value of our available-for-sale fixed-maturity securities by contractual maturity are as follows (in millions):

	September 30, 2013
	Amortized Cost		Fair Value
Due in one year or less	$	588.1	$	588.4
Due after one year through two years		267.7		267.6
Total	$	855.8	$	856.0