Investments (Tables)

3 Months Ended

Mar. 31, 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 Cost		Gross Unrealized					Fair value
			Gains		Losses
As of March 31, 2013
Corporate debt securities	$	401.5	$	0.3	$	(0.2	)	$	401.6
U.S. government and agency debt securities		263.8		0.1		—			263.9
Foreign government debt securities		5.0		—		—			5.0
Commercial paper		16.0		—		—			16.0
Certificates of deposit		89.2		0.1		—			89.3
Total short and long-term investments	$	775.5	$	0.5	$	(0.2	)	$	775.8
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):

	March 31, 2013					December 31, 2012
	Fair Value		Unrealized Losses			Fair value		Unrealized Losses
Corporate debt securities	$	154.0	$	(0.2	)	$	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):

	March 31, 2013
	Amortized Cost		Fair Value
Due in one year or less	$	543.9	$	544.2
Due after one year through two years		231.6		231.6
Total	$	775.5	$	775.8