Investments (Tables)

3 Months Ended

Mar. 31, 2012

Investments [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 March 31, 2012
Corporate debt securities	$	331.1	$	0.4	$	(0.1	)	$	331.4
U.S. government and agency debt securities		200.5		—		(0.1	)		200.4
Foreign government debt securities		2.8		—		—			2.8
Commercial paper		127.3		—		—			127.3
Certificates of deposit		90.1		—		—			90.1
Total short and long-term investments	$	751.8	$	0.4	$	(0.2	)	$	752.0
As of December 31, 2011
Corporate debt securities	$	324.8	$	0.2	$	(0.3	)	$	324.7
U.S. government and agency debt securities		177.1		0.1		—			177.2
Municipal bonds		1.0		—		—			1.0
Foreign government debt securities		6.8		—		—			6.8
Commercial paper		74.5		—		—			74.5
Certificates of deposit		88.5		—		—			88.5
Total short and long-term investments	$	672.7	$	0.3	$	(0.3	)	$	672.7

Fair values and gross unrealized losses for all available-for-sale securities in an 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):

	March 31, 2012					December 31, 2011
	Fair Value		Unrealized Losses			Fair value		Unrealized Losses
Corporate debt securities	$	131.1	$	(0.1	)	$	164.5	$	(0.3	)
U.S. government and agency debt securities		173.0		(0.1	)		—		—
Total	$	304.1	$	(0.2	)	$	164.5	$	(0.3	)

The 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):

	March 31, 2012
	Amortized Cost		Fair Value
Due in one year or less	$	555.0	$	555.1
Due after one year through two years		196.8		196.9
Total	$	751.8	$	752.0