Available-for-sale securities (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Summary of Available-for-sale debt and equity securities at estimated fair value

The following summarizes our available-for-sale securities (in millions):

	December 31, 2017									December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Corporate debt securities	$	14,790	$	3	$	(46	)	$	14,747	$	12,657	$	7	$	(61	)	$	12,603
Certificates of deposit	5,131		—		—			5,131		943		—		—			943
Money market funds	4,714		—		—			4,714		5,464		—		—			5,464
U.S. treasury securities	4,090		—		(29		)	4,061		5,558		1		(30		)	5,529
Residential mortgage and asset-backed securities	4,072		1		(15		)	4,058		3,613		2		(13		)	3,602
U.S. government agencies securities	934		—		(8		)	926		981		—		(6		)	975
Non-U.S. government securities	668		—		(4		)	664		725		—		(5		)	720
Municipal debt securities	—		—		—			—		27		—		—			27
Equity securities	357		278		—			635		357		71		—			428
Total	$	34,756	$	282	$	(102	)	$	34,936	$	30,325	$	81	$	(115	)	$	30,291

Summary of the classification of available-for-sale debt and equity securities

The following table summarizes the classification of our available-for-sale securities on our Consolidated Balance Sheets (in millions):

	December 31, 2017		December 31, 2016
Cash and cash equivalents	$	5,195	$	5,712
Short-term marketable securities	17,922		3,666
Prepaid and other current assets	635		—
Long-term marketable securities	11,184		20,485
Other long-term assets	—		428
Total	$	34,936	$	30,291

Summary of available-for-sale securities by contractual maturity

The following table summarizes our available-for-sale securities by contractual maturity (in millions):

	December 31, 2017
	Amortized Cost		Fair Value
Within one year	$	23,139	$	23,117
After one year through five years	11,125		11,051
After five years through ten years	98		96
After ten years	37		37
Total	$	34,399	$	34,301

Summary of available-for-sale debt securities in a continuous loss position deemed not to be other-than-temporarily impaired

The following table summarizes our available-for-sale securities that were in a continuous unrealized loss position, but were not deemed to be other-than-temporarily impaired (in millions):

	Less Than 12 Months					12 Months or Greater					Total
	Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value		Gross Unrealized Losses			Estimated Fair Value
December 31, 2017
Corporate debt securities	$	(14	)	$	7,674	$	(32	)	$	3,561	$	(46	)	$	11,235
U.S. treasury securities	(2		)	821		(27		)	3,240		(29		)	4,061
Residential mortgage and asset-backed securities	(4		)	2,245		(11		)	1,206		(15		)	3,451
U.S. government agencies securities	(1		)	206		(7		)	700		(8		)	906
Non-U.S. government securities	(1		)	203		(3		)	461		(4		)	664
Total	$	(22	)	$	11,149	$	(80	)	$	9,168	$	(102	)	$	20,317
December 31, 2016
Corporate debt securities	$	(60	)	$	8,685	$	(1	)	$	155	$	(61	)	$	8,840
U.S. treasury securities	(30		)	5,081		—			—		(30		)	5,081
Residential mortgage and asset-backed securities	(13		)	2,180		—			42		(13		)	2,222
U.S. government agencies securities	(6		)	897		—			—		(6		)	897
Non-U.S. government securities	(5		)	714		—			5		(5		)	719
Certificates of deposit	—			15		—			—		—			15
Municipal debt securities	—			11		—			—		—			11
Total	$	(114	)	$	17,583	$	(1	)	$	202	$	(115	)	$	17,785