Investments (Tables)

6 Months Ended

Jun. 30, 2015

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, 2015
Corporate debt securities	$	433.1	$	0.2	$	(0.2	)	$	433.1
U.S. government and agency debt securities		121.9		—		—			121.9
Commercial paper		34.4		—		—			34.4
Certificates of deposit		31.0		—		—			31.0
Total short and long-term investments	$	620.4	$	0.2	$	(0.2	)	$	620.4
As of December 31, 2014
Corporate debt securities	$	516.9	$	0.1	$	(0.5	)	$	516.5
U.S. government and agency debt securities		194.3		—		—			194.3
Commercial paper		57.8		—		—			57.8
Certificates of deposit		100.3		—		—			100.3
Total short and long-term investments	$	869.3	$	0.1	$	(0.5	)	$	868.9

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, 2015
	Amortized Cost		Fair Value
Due in one year or less	$	459.0	$	459.0
Due after one year through two years		161.4		161.4
Total	$	620.4	$	620.4