Investments

The following tables summarize the unrealized gains and losses and estimated fair value of our investments classified as available-for-sale as of March 31, 2017 and December 31, 2016 (in millions):



	March 31, 2017
	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term investments:
Restricted cash	$	20	$	—	$	—		$	20
Corporate debt securities ⁽¹⁾	4,670		19		(2		)	4,687
Government and agency securities	64		4		—			68
	$	4,754	$	23	$	(2	)	$	4,775
Long-term investments:
Corporate debt securities ⁽¹⁾	4,411		18		(8		)	4,421
	$	4,411	$	18	$	(8	)	$	4,421


(1)	As of March 31, 2017, investment securities with a fair value of $711 million and a net unrealized foreign exchange gain of $20 million were held by a foreign subsidiary in which the U.S. dollar is not the functional currency.



	December 31, 2016
	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term investments:
Restricted cash	$	19	$	—	$	—		$	19
Corporate debt securities	5,203		44		(1		)	5,246
Government and agency securities	63		5		—			68
	$	5,285	$	49	$	(1	)	$	5,333
Long-term investments:
Corporate debt securities	3,848		15		(12		)	3,851
	$	3,848	$	15	$	(12	)	$	3,851

Investment securities in a continuous loss position for greater than 12 months had an estimated fair value of $27 million and an immaterial amount of unrealized losses as of March 31, 2017 and an estimated fair value of $123 million and an immaterial amount of unrealized losses as of December 31, 2016. Refer to “Note 13 - Accumulated Other Comprehensive Income” for amounts reclassified to earnings from unrealized gains and losses.

The estimated fair values of our short-term and long-term investments classified as available-for-sale by date of contractual maturity as of March 31, 2017 are as follows (in millions):



	March 31, 2017
One year or less (including restricted cash of $20)	$	4,775
One year through two years	1,931
Two years through three years	1,743
Three years through four years	296
Four years through five years	451
	$	9,196

Equity and cost method investments

We have made multiple equity and cost method investments, which are reported in long-term investments on our condensed consolidated balance sheet. As of March 31, 2017 and December 31, 2016, our equity and cost method investments totaled $119 million and $118 million, respectively.