Investments (Tables)

6 Months Ended

Jun. 30, 2011

Investments [Abstract]

Investments in short and long-term classified as available-for-sale securities

	Amortized		Gross Unrealized
	Cost		Gains		Losses			Fair value
As of June 30, 2011
Corporate debt securities	$	240.4	$	0.3	$	(0.1	)	$	240.6
U.S. government and agency debt securities		37.9		—		—			37.9
Municipal bonds		1.0		—		—			1.0
Foreign government debt securities		7.5		—		—			7.5
Commercial paper		9.5		—		—			9.5
Certificates of deposit		129.1		0.1		—			129.2
Total short and long-term investments	$	425.4	$	0.4	$	(0.1	)	$	425.7
As of December 31, 2010
Corporate debt securities	$	203.9	$	0.1	$	(0.2	)	$	203.8
U.S. government and agency debt securities		47.9		—		—			47.9
Municipal bonds		1.1		—		—			1.1
Foreign government debt securities		10.3		—		—			10.3
Commercial paper		16.1		—		—			16.1
Certificates of deposit		131.5		—		(0.1	)		131.4
Total short and long-term investments	$	410.8	$	0.1	$	(0.3	)	$	410.6

Fair values and gross unrealized losses for all available-for-sale securities in an unrealized loss position deemed to be temporary

	As of June 30, 2011					As of December 31, 2010
			Unrealized					Unrealized
	Fair Value		Losses			Fair value		Losses
Corporate debt securities	$	62.4	$	(0.1	)	$	126.1	$	(0.2	)
Certificates of deposit		—		—			50.6		(0.1	)
Total	$	62.4	$	(0.1	)	$	176.7	$	(0.3	)

The cost and fair value of available-for-sale fixed-maturity securities by contractual maturity

	As of June 30, 2011
	Amortized
	Cost		Fair Value
Due in one year or less	$	321.2	$	321.4
Due after one year through two years		104.2		104.3
Total	$	425.4	$	425.7