Investments (Tables)

6 Months Ended

Jun. 30, 2014

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 June 30, 2014
Corporate debt securities	$	323.6	$	0.3	$	(0.1	)	$	323.8
U.S. government and agency debt securities		185.1		—		—			185.1
Foreign government debt securities		8.1		—		—			8.1
Commercial paper		314.6		—		—			314.6
Certificates of deposit		65.2		—		—			65.2
Total short and long-term investments	$	896.6	$	0.3	$	(0.1	)	$	896.8
As of December 31, 2013
Corporate debt securities	$	457.6	$	0.4	$	(0.1	)	$	457.9
U.S. government and agency debt securities		211.1		0.1		—			211.2
Foreign government debt securities		3.1		—		—			3.1
Commercial paper		68.3		—		—			68.3
Certificates of deposit		67.2		—		—			67.2
Total short and long-term investments	$	807.3	$	0.5	$	(0.1	)	$	807.7

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):

	June 30, 2014
	Amortized Cost		Fair Value
Due in one year or less	$	729.3	$	729.3
Due after one year through two years		167.3		167.5
Total	$	896.6	$	896.8