Investments (Tables)

12 Months Ended

Dec. 31, 2018

Investments [Abstract]

Fair value of short and long-term investments classified as available for sale

December 31, 2018 and 2017 (in millions):

	December 31, 2018
	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term investments:
Restricted cash	$	17	$	—	$	—		$	17
Corporate debt securities	2,615		—		(9		)	2,606
Government and agency securities	90		—		—			90
	$	2,722	$	—	$	(9	)	$	2,713
Long-term investments:
Corporate debt securities	3,682		1		(48		)	3,635
	$	3,682	$	1	$	(48	)	$	3,635

	December 31, 2017
	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term investments:
Restricted cash	$	20	$	—	$	—		$	20
Corporate debt securities	3,726		1		(4		)	3,723
	$	3,746	$	1	$	(4	)	$	3,743
Long-term investments:
Corporate debt securities	5,458		12		(24		)	5,446
	$	5,458	$	12	$	(24	)	$	5,446

Estimated fair values of short and long-term investments classified as available for sale by date of contractual maturity

The estimated fair values of our short-term and long-term investments classified as available-for-sale by date of contractual maturity as of December 31, 2018 are as follows (in millions):  

	December 31, 2018
One year or less (including restricted cash of $17)	$	2,713
One year through two years	1,922
Two years through three years	1,123
Three years through four years	473
Four years through five years	117
Thereafter	—
Total	$	6,348

Schedule of Equity Investments

The following table provides a summary of our equity investments as of December 31, 2018 and December 31, 2017 (in millions):

	December 31, 2018		December 31, 2017
Equity investments without readily determinable fair values	$	137	$	872
Equity investments under the equity method of accounting	6		13
Total equity investments	$	143	$	885

Schedule of Unrealized Gains and Losses

The following table provides a summary of unrealized gains and losses recorded in interest and other, net during the twelve months ended December 31, 2018 related to equity investments without readily determinable fair values still held at December 31, 2018.

	Year Ended December 31, 2018
Net gains/(losses) recognized during the period on equity investments	$	313
Less: Net gains/(losses) recognized during the period on equity investments sold during the period	(313		)
Total unrealized gains/(losses) on equity investments still held at December 31, 2018	$	—

Schedule of Investments without Readily Determinable Fair Value

The following table summarizes the total carrying value of equity investments without readily determinable fair values during the twelve months ended December 31, 2018 (in millions):

	Year Ended December 31, 2018
Carrying value, beginning of period	$	872
Additions	23
Sales	(718		)
Downward adjustments for observable price changes and impairment	(20		)
Foreign currency translation and other	(20		)
Carrying value, end of period	$	137