Financial Instruments

Marketable Securities

The following tables summarize our marketable debt and equity securities:



As of March 31, 2013 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses		Amortized Cost
Available-for-sale:
Corporate debt securities
Current	$	—	$	—	$	—	$	—
Non-current	—		—		—		—
Government securities
Current	—		—		—		—
Non-current	—		—		—		—
Mortgage and other asset backed securities
Current	—		—		—		—
Non-current	—		—		—		—
Total marketable debt securities	$	—	$	—	$	—	$	—
Marketable equity securities, non-current	$	11.6	$	4.9	$	—	$	6.7



As of December 31, 2012 (In millions)	Fair Value		Gross Unrealized Gains		Gross Unrealized Losses			Amortized Cost
Available-for-sale:
Corporate debt securities
Current	$	346.9	$	0.3	$	—		$	346.6
Non-current	654.1		2.8		(0.6		)	651.9
Government securities
Current	783.4		0.3		—			783.1
Non-current	874.4		0.8		—			873.6
Mortgage and other asset backed securities
Current	4.8		—		—			4.8
Non-current	508.1		1.4		(1.3		)	508.0
Total marketable debt securities	$	3,171.7	$	5.6	$	(1.9	)	$	3,168.0
Marketable equity securities, non-current	$	9.0	$	3.0	$	—		$	6.0

The following table summarizes our financial assets with maturities of less than 90 days from the date of purchase included within cash and cash equivalents on the accompanying condensed consolidated balance sheet:



(In millions)	As of March 31, 2013		As of December 31, 2012
Commercial paper	$	—	$	40.7
Overnight repurchase agreements	—		67.4
Short-term debt securities	358.6		331.3
Total	$	358.6	$	439.4

The carrying values of our commercial paper, including accrued interest, overnight repurchase agreements, and our short-term debt securities approximate fair value.

Summary of Contractual Maturities: Available-for-Sale Securities

The estimated fair value and amortized cost of our marketable debt securities available-for-sale by contractual maturity are summarized as follows:



	As of March 31, 2013				As of December 31, 2012
(In millions)	Estimated Fair Value		Amortized Cost		Estimated Fair Value		Amortized Cost
Due in one year or less	$	—	$	—	$	1,135.0	$	1,134.5
Due after one year through five years	—		—		1,744.3		1,741.2
Due after five years	—		—		292.4		292.3
Total available-for-sale securities	$	—	$	—	$	3,171.7	$	3,168.0

The average maturity of our marketable debt securities available-for-sale as of December 31, 2012 was 14 months.

Proceeds from Marketable Debt Securities

The proceeds from maturities and sales of marketable debt securities and resulting realized gains and losses are summarized as follows:



	For the Three Months Ended March 31,
(In millions)	2013			2012
Proceeds from maturities and sales	$	4,329.5		$	824.4
Realized gains	$	6.3		$	0.7
Realized losses	$	(2.0	)	$	(0.7	)

Strategic Investments

As of March 31, 2013 and December 31, 2012, our strategic investment portfolio was comprised of investments totaling $64.4 million and $64.2 million, respectively, which are included in investments and other assets in our accompanying condensed consolidated balance sheets.

Our strategic investment portfolio includes investments in marketable equity securities of certain biotechnology companies and our investments in venture capital funds accounted for at fair value which totaled $29.6 million and $29.3 million as of March 31, 2013 and December 31, 2012, respectively. Our strategic investment portfolio also includes other equity investments in privately-held companies and additional investments in venture capital funds accounted for under the cost method. The carrying value of these investments totaled $34.8 million and $34.9 million as of March 31, 2013 and December 31, 2012, respectively.

Net Gains, Impairments and Changes to Fair Value

During the three months ended March 31, 2013 and 2012, we realized net losses, impairments and changes to fair value recorded through income of $0.3 million and net gains of $11.3 million, respectively, on our strategic investment portfolio. The net gains recognized during the three months ended March 31, 2012 included a gain of $9.0 million recognized upon our acquisition of Stromedix as we previously held an equity interest. For a more detailed description of this transaction, please read Note 2, Acquisitions to our consolidated financial statements included within our 2012 Form 10-K.

Impairments

For the three months ended March 31, 2013 and 2012, we recognized impairment charges on our marketable equity securities of certain biotechnology companies, investments in venture capital funds accounted for under the cost method and investments in privately-held companies totaling $0.3 million and $0.5 million, respectively.