Investments (Tables)

6 Months Ended

Jun. 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		Gross Unrealized
	Cost		Gains		Losses			Fair value
As of June 30, 2013
Corporate debt securities	$	392.7	$	0.1	$	(0.8	)	$	392.0
U.S. government and agency debt securities		271.6		0.1		(0.1	)		271.6
Commercial paper		49.0		—		—			49.0
Certificates of deposit		87.4		0.1		—			87.5
Total short and long-term investments	$	800.7	$	0.3	$	(0.9	)	$	800.1
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 all available-for-sale securities in an unrealized loss position deemed to be temporary (in millions):

	June 30, 2013					December 31, 2012
	Fair Value		Unrealized Losses			Fair value		Unrealized Losses
Corporate debt securities	$	251.6	$	(0.8	)	$	144.2	$	(0.1	)
U.S. government and agency debt securities		161.5		(0.1	)		—		—
Total	$	413.1	$	(0.9	)	$	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):

	June 30, 2013
	Amortized Cost		Fair Value
Due in one year or less	$	525.9	$	525.9
Due after one year through two years		274.8		274.2
Total	$	800.7	$	800.1