Investments (Tables)

9 Months Ended

Sep. 30, 2011

Investments [Abstract]

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

	Amortized Cost		Gross Unrealized					Fair value
			Gains		Losses
As of September 30, 2011
Corporate debt securities	$	308.8	$	0.1	$	(0.3	)	$	308.6
U.S. government and agency debt securities		83.9		—		—			83.9
Municipal bonds		1.0		—		—			1.0
Foreign government debt securities		7.5		—		—			7.5
Commercial paper		49.5		—		—			49.5
Certificates of deposit		135.5		0.1		—			135.6
Total short and long-term investments	$	586.2	$	0.2	$	(0.3	)	$	586.1
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 September 30, 2011					As of December 31, 2010
	Fair Value		Unrealized Losses			Fair value		Unrealized Losses
Corporate debt securities	$	169.4	$	(0.3	)	$	126.1	$	(0.2	)
Certificates of deposit		—		—			50.6		(0.1	)
Total	$	169.4	$	(0.3	)	$	176.7	$	(0.3	)

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

	As of September 30, 2011
	Amortized Cost		Fair Value
Due in one year or less	$	424.8	$	424.9
Due after one year through two years		161.4		161.2
Total	$	586.2	$	586.1