Investments (Tables)

6 Months Ended

Jun. 30, 2012

Investments [Abstract]

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

	Amortized Cost		Gross Unrealized
			Gains		Losses			Fair value
As of June 30, 2012
Corporate debt securities	$	296.3	$	0.3	$	(0.1	)	$	296.5
U.S. government and agency debt securities		230.5		—		—			230.5
Foreign government debt securities		2.8		—		—			2.8
Commercial paper		183.3		—		—			183.3
Certificates of deposit		70.7		0.1		—			70.8
Total short and long-term investments	$	783.6	$	0.4	$	(0.1	)	$	783.9
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

	June 30, 2012					December 31, 2011
	Fair Value		Unrealized Losses			Fair value		Unrealized Losses
Corporate debt securities	$	118.5	$	(0.1	)	$	164.5	$	(0.3	)

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

	June 30, 2012
	Amortized Cost		Fair Value
Due in one year or less	$	684.6	$	684.9
Due after one year through two years		99.0		99.0
Total	$	783.6	$	783.9